[LeetCode]202. Happy Number 快乐数

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

1版：

将各个位之和存在数组里，如果有重复就不是快乐数。

class Solution {public:bool isHappy(int n){if (n == 0)return 0;if (n == 1)return 1;int temp[400];int t = 0;while (n  > 0){int i = 0;while (n > 0){i = i + (n % 10)*(n % 10);n /= 10;}for (int j = 0; j < t; j++){if (temp[j] == i) return false;}temp[t] = i;t++;if (i == 1)return true;else n = i;}}};

2版：

别人的Solution中看到。

如果是快乐数，后者肯定会追上前者，如果不是，进入重复的循环也会到一样。

class Solution {public:    int next (int n)    {        int sum = 0;        while(n)        {            sum += (n % 10)*(n % 10);            n /= 10;        }        return sum ;    }    bool isHappy(int num)     {        int a = num;        int b = next(num);        while (a != b)        {            a = next(a);            b = next(next(b));        }        return a==1;    }};