#Happy Number ##Problem: Write an algorithm to determine if a number is "happy".
A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.
Example: 19 is a happy number
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
##Idea:
Two Pointers循环链
class Solution {
public:
bool isHappy(int n) {
int slow=n;
int fast=n;
while(fast!=1)
{
slow=sumOfSquare(slow);
fast=sumOfSquare(fast);
fast=sumOfSquare(fast);
if(slow==fast&&fast!=1) return false;
}
return true;
}
private:
int sumOfSquare(int n)
{
int sum=0;
while(n)
{
sum += (n%10)*(n%10);
n /= 10;
}
return sum;
}
};##To Study:
Hash Table
class Solution {
public:
bool isHappy(int n) {
unordered_set<int> record;
n=sumOfSquare(n);
if(n==1) return true;
while(record.find(n)==record.end())
{
record.insert(n);
n=sumOfSquare(n);
if(n==1) return true;
}
return false;
}
private:
int sumOfSquare(int n)
{
int sum=0;
while(n)
{
sum += (n%10)*(n%10);
n /= 10;
}
return sum;
}
};