problem 053

Author: TipsyPixie

problem053/README.md

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+## Daily Coding Problem: Problem #53
+
+
+Good morning! Here's your coding interview problem for today.
+
+This problem was asked by Apple.
+
+Implement a queue using two stacks. Recall that a queue is a FIFO (first-in, first-out) data structure with the following methods: enqueue, which inserts an element into the queue, and dequeue, which removes it.

problem053/problem053.go

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+package problem053
+
+type stack struct {
+	capacity int
+	data     []int
+}
+
+func newStack(capacity int) *stack {
+	return &stack{
+		capacity: capacity,
+		data:     make([]int, 0, capacity),
+	}
+}
+
+func (thisStack *stack) isEmpty() bool {
+	return len(thisStack.data) == 0
+}
+
+func (thisStack *stack) push(v int) *stack {
+	if len(thisStack.data) >= thisStack.capacity {
+		panic("max length exceeded")
+	}
+	thisStack.data = append(thisStack.data, v)
+	return thisStack
+}
+
+func (thisStack *stack) pop() int {
+	if len(thisStack.data) == 0 {
+		panic("stack empty")
+	}
+	v := thisStack.data[len(thisStack.data)-1]
+	thisStack.data = thisStack.data[:len(thisStack.data)-1]
+	return v
+}
+
+type queue struct {
+	incomingStack *stack
+	outgoingStack *stack
+}
+
+func NewQueue(capacity int) *queue {
+	return &queue{
+		incomingStack: newStack(capacity),
+		outgoingStack: newStack(capacity),
+	}
+}
+
+func (thisQueue *queue) Enqueue(v int) *queue {
+	for !thisQueue.outgoingStack.isEmpty() {
+		thisQueue.incomingStack.push(thisQueue.outgoingStack.pop())
+	}
+	thisQueue.incomingStack.push(v)
+	return thisQueue
+}
+
+func (thisQueue *queue) Dequeue() int {
+	for !thisQueue.incomingStack.isEmpty() {
+		thisQueue.outgoingStack.push(thisQueue.incomingStack.pop())
+	}
+	return thisQueue.outgoingStack.pop()
+
+}

problem053/problem053_test.go

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+package problem053
+
+import "testing"
+
+func TestQueue(t *testing.T) {
+	q := NewQueue(16)
+	for i := 0; i < 8; i++ {
+		q.Enqueue(i)
+	}
+
+	for i := 0; i < 8; i++ {
+		if v := q.Dequeue(); v != i {
+			t.Logf("%d != %d", v, i)
+			t.Fail()
+		}
+	}
+}