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‎README.md

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2020

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## Problems
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| Number | Difficulty | Asked By | Title |
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|-------------------|------------|-------------|--------------------------------------------------------------|
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| [#1](problem001) | EASY | Google | Finding 2 numbers that adds up to k |
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| [#2](problem002) | HARD | Uber | Array multiplication |
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| [#3](problem003) | MEDIUM | Google | Tree serialization |
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| [#4](problem004) | HARD | Stripe | Finding lowest positive number |
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| [#5](problem005) | MEDIUM | Jane Street | Lisp pair operations |
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| [#6](problem006) | HARD | Google | XOR linked list |
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| [#7](problem007) | MEDIUM | Facebook | |
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| [#8](problem008) | EASY | Google | |
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| [#9](problem009) | HARD | Airbnb | |
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| [#10](problem010) | MEDIUM | Apple | |
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| [#11](problem011) | MEDIUM | Twitter | |
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| [#12](problem012) | HARD | Amazon | |
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| [#13](problem013) | HARD | Amazon | |
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| [#14](problem014) | MEDIUM | Google | |
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| [#15](problem015) | MEDIUM | Facebook | |
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| [#16](problem016) | EASY | Twitter | |
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| [#17](problem017) | HARD | Google | |
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| [#18](problem018) | HARD | Google | |
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| [#19](problem019) | MEDIUM | Facebook | |
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| [#20](problem020) | EASY | Google | |
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| [#21](problem021) | EASY | Snapchat | |
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| [#22](problem022) | MEDIUM | Microsoft | |
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| [#23](problem023) | EASY | Google | |
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| [#24](problem024) | MEDIUM | Google | |
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| [#25](problem025) | HARD | Facebook | |
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| [#26](problem026) | MEDIUM | Google | |
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| [#27](problem027) | EASY | Facebook | |
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| [#28](problem028) | MEDIUM | Palantir | |
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| [#29](problem029) | EASY | Amazon | |
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| [#30](problem030) | MEDIUM | Facebook | |
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| [#31](problem031) | EASY | Google | |
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| [#32](problem032) | HARD | Jane Street | |
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| [#33](problem033) | EASY | Microsoft | |
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| [#34](problem034) | MEDIUM | Quora | |
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| [#35](problem035) | HARD | Google | Segregating R, G, and Bs in linear time |
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| [#36](problem036) | MEDIUM | Dropbox | Finding the second largest node in BST |
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| [#37](problem037) | EASY | Google | Generating the power set of a set |
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| [#38](problem038) | HARD | Microsoft | Arranging N queens without threatening one another |
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| [#39](problem039) | MEDIUM | Dropbox | Conway's Game of Life |
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| [#40](problem040) | HARD | Google | Finding the non-duplicated number |
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| [#41](problem041) | MEDIUM | Facebook | Finding full itinerary from a list of flights |
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| [#42](problem042) | HARD | Google | Finding a subset of S that adds up to k |
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| [#43](problem043) | EASY | Amazon | Implementing Stack |
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| [#44](problem044) | MEDIUM | Google | Counting inversions in a list of numbers |
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| [#45](problem045) | EASY | Two Sigma | Writing rand function |
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| [#46](problem046) | HARD | Amazon | Finding the longest palindromic substring |
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| [#47](problem047) | EASY | Facebook | Calculating maximum profit with chronological stock prices |
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| [#48](problem048) | MEDIUM | Google | Building a tree with given pre-order and in-order traversals |
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| [#49](problem049) | MEDIUM | Amazon | Finding the maximum sum of contiguous subarray |
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| [#50](problem050) | EASY | Microsoft | Arithmetic binary tree |
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| [#51](problem051) | MEDIUM | Facebook | Card shuffle |
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| [#52](problem052) | HARD | Google | LRU cache |
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| [#53](problem053) | MEDIUM | Apple | Implementing a queue with 2 stacks |
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| [#54](problem054) | HARD | Dropbox | Implementing a Sudoku solver |
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| [#55](problem055) | EASY | Microsoft | URL shortener |
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| [#56](problem056) | MEDIUM | Google | Map coloring |
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| [#57](problem057) | MEDIUM | Amazon | Splitting string into lines of limited length |
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| [#58](problem058) | MEDIUM | Amazon | Search in rotated sorted array |
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| [#59](problem059) | HARD | Google | Low bandwidth file synchronization |
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| [#60](problem060) | MEDIUM | Facebook | Partitioning set by subtotals |
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| Number | Difficulty | Asked By | Title |
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|-------------------|------------|-------------|---------------------------------------------------------------|
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| [#1](problem001) | EASY | Google | Finding 2 numbers that adds up to k |
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| [#2](problem002) | HARD | Uber | Array multiplication |
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| [#3](problem003) | MEDIUM | Google | Tree serialization |
28+
| [#4](problem004) | HARD | Stripe | Finding lowest positive number |
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| [#5](problem005) | MEDIUM | Jane Street | Lisp pair operations |
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| [#6](problem006) | HARD | Google | XOR linked list |
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| [#7](problem007) | MEDIUM | Facebook | |
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| [#8](problem008) | EASY | Google | |
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| [#9](problem009) | HARD | Airbnb | |
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| [#10](problem010) | MEDIUM | Apple | |
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| [#11](problem011) | MEDIUM | Twitter | |
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| [#12](problem012) | HARD | Amazon | |
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| [#13](problem013) | HARD | Amazon | |
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| [#14](problem014) | MEDIUM | Google | |
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| [#15](problem015) | MEDIUM | Facebook | |
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| [#16](problem016) | EASY | Twitter | |
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| [#17](problem017) | HARD | Google | |
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| [#18](problem018) | HARD | Google | |
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| [#19](problem019) | MEDIUM | Facebook | |
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| [#20](problem020) | EASY | Google | |
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| [#21](problem021) | EASY | Snapchat | |
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| [#22](problem022) | MEDIUM | Microsoft | |
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| [#23](problem023) | EASY | Google | |
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| [#24](problem024) | MEDIUM | Google | |
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| [#25](problem025) | HARD | Facebook | |
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| [#26](problem026) | MEDIUM | Google | |
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| [#27](problem027) | EASY | Facebook | |
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| [#28](problem028) | MEDIUM | Palantir | |
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| [#29](problem029) | EASY | Amazon | |
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| [#30](problem030) | MEDIUM | Facebook | |
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| [#31](problem031) | EASY | Google | |
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| [#32](problem032) | HARD | Jane Street | |
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| [#33](problem033) | EASY | Microsoft | |
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| [#34](problem034) | MEDIUM | Quora | |
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| [#35](problem035) | HARD | Google | Segregating R, G, and Bs in linear time |
60+
| [#36](problem036) | MEDIUM | Dropbox | Finding the second largest node in BST |
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| [#37](problem037) | EASY | Google | Generating the power set of a set |
62+
| [#38](problem038) | HARD | Microsoft | Arranging N queens without threatening one another |
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| [#39](problem039) | MEDIUM | Dropbox | Conway's Game of Life |
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| [#40](problem040) | HARD | Google | Finding the non-duplicated number |
65+
| [#41](problem041) | MEDIUM | Facebook | Finding full itinerary from a list of flights |
66+
| [#42](problem042) | HARD | Google | Finding a subset of S that adds up to k |
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| [#43](problem043) | EASY | Amazon | Implementing Stack |
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| [#44](problem044) | MEDIUM | Google | Counting inversions in a list of numbers |
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| [#45](problem045) | EASY | Two Sigma | Writing rand function |
70+
| [#46](problem046) | HARD | Amazon | Finding the longest palindromic substring |
71+
| [#47](problem047) | EASY | Facebook | Calculating maximum profit with chronological stock prices |
72+
| [#48](problem048) | MEDIUM | Google | Building a tree with given pre-order and in-order traversals |
73+
| [#49](problem049) | MEDIUM | Amazon | Finding the maximum sum of contiguous subarray |
74+
| [#50](problem050) | EASY | Microsoft | Arithmetic binary tree |
75+
| [#51](problem051) | MEDIUM | Facebook | Card shuffle |
76+
| [#52](problem052) | HARD | Google | LRU cache |
77+
| [#53](problem053) | MEDIUM | Apple | Implementing a queue with 2 stacks |
78+
| [#54](problem054) | HARD | Dropbox | Implementing a Sudoku solver |
79+
| [#55](problem055) | EASY | Microsoft | URL shortener |
80+
| [#56](problem056) | MEDIUM | Google | Map coloring |
81+
| [#57](problem057) | MEDIUM | Amazon | Splitting string into lines of limited length |
82+
| [#58](problem058) | MEDIUM | Amazon | Search in rotated sorted array |
83+
| [#59](problem059) | HARD | Google | Low bandwidth file synchronization |
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| [#60](problem060) | MEDIUM | Facebook | Partitioning set by subtotals |
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| [#61](problem061) | MEDIUM | Google | Faster pow operation |
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| [#62](problem062) | MEDIUM | Facebook | Couting methods to move down |

‎problem061/README.md

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## Daily Coding Problem: Problem #61
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Good morning! Here's your coding interview problem for today.
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This problem was asked by Google.
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Implement integer exponentiation. That is, implement the pow(x, y) function, where x and y are integers and returns x^y.
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Do this faster than the naive method of repeated multiplication.
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For example, pow(2, 10) should return 1024.

‎problem061/problem061.go

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package problem061
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func PowSimple(base int, exponent int) int {
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result := 1
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for i := 0; i < exponent; i++ {
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result *= base
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}
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return result
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}
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func PowFaster(base int, exponent int) int {
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result := 1
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modifiedExponent, modifiedBase := exponent, base
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for modifiedExponent > 1 {
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if modifiedExponent&1 == 1 {
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result *= modifiedBase
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}
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modifiedExponent >>= 1
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modifiedBase *= modifiedBase
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}
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return result * modifiedBase
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}

‎problem061/problem061_test.go

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package problem061
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import (
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"testing"
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)
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type argumentSet struct {
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base int
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exponent int
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result int
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}
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func assert(t *testing.T, actual int, expected int) bool {
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t.Logf("Actual: %d / Expected: %d", actual, expected)
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if actual != expected {
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return false
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}
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return true
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}
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func getBenchmark(pow func(int, int) int, base int, exponent int) func(*testing.B) {
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return func(b *testing.B) {
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for i := 0; i < b.N; i++ {
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pow(base, exponent)
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}
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}
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}
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func TestPow(t *testing.T) {
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testCases := []argumentSet{
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{
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base: 8,
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exponent: 19,
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},
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}
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for _, testCase := range testCases {
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if !assert(t, PowFaster(testCase.base, testCase.exponent), PowSimple(testCase.base, testCase.exponent)) {
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t.FailNow()
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}
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resultFaster := testing.Benchmark(getBenchmark(PowFaster, testCase.base, testCase.exponent))
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resultSimple := testing.Benchmark(getBenchmark(PowSimple, testCase.base, testCase.exponent))
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if resultSimple.T.Milliseconds() < resultFaster.T.Milliseconds() {
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t.Logf("repeated multiplication took %d, shift took %d", resultSimple.T.Milliseconds(), resultFaster.T.Milliseconds())
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t.FailNow()
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}
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}
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}

‎problem062/README.md

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## Daily Coding Problem: Problem #62
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Good morning! Here's your coding interview problem for today.
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This problem was asked by Facebook.
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There is an N by M matrix of zeroes. Given N and M, write a function to count the number of ways of starting at the top-left corner and getting to the bottom-right corner. You can only move right or down.
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For example, given a 2 by 2 matrix, you should return 2, since there are two ways to get to the bottom-right:
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```text
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Right, then down
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Down, then right
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```
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Given a 5 by 5 matrix, there are 70 ways to get to the bottom-right.

‎problem062/problem062.go

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package problem062
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func CountWay(rowCount int, columnCount int) int {
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return combination(rowCount+columnCount-2, rowCount-1)
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}
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func combination(n int, m int) int {
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dividendChannel := make(chan int, 1)
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divisorChannel := make(chan int, 1)
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go func() {
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a := 1
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for b := n; b > m; b-- {
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a *= b
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}
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dividendChannel <- a
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}()
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go func() {
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a := 1
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for b := m; b > 0; b-- {
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a *= b
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}
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divisorChannel <- a
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}()
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result := 1
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select {
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case dividend := <-dividendChannel:
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result *= dividend
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}
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select {
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case divisor := <-divisorChannel:
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result /= divisor
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}
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return result
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}

‎problem062/problem062_test.go

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package problem062
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import "testing"
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type argumentSet struct {
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rowCount int
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columnCount int
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result int
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}
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func assert(t *testing.T, actual int, expected int) bool {
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if actual != expected {
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t.Logf("Actual: %v / Expected: %v", actual, expected)
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return false
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}
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return true
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}
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func TestCountWay(t *testing.T) {
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testCases := []argumentSet{
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{
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rowCount: 2,
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columnCount: 2,
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result: 2,
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},
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{
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rowCount: 5,
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columnCount: 5,
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result: 70,
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},
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}
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for _, testCase := range testCases {
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if !assert(t, CountWay(testCase.rowCount, testCase.columnCount), testCase.result) {
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t.FailNow()
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}
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}
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}

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