LeetCode 202. Happy Number

202. Happy Number

Description

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

Solution

• 题意即判断一个数是不是“Happy Num”，即给定数用各位平方和代替，不断重复，最后能否得到1。如果能够得到，就返回true，否则返回false
• 先写一个子函数计算各位平方和，然后再用循环判断是否满足，设定一个上界如果超过我们便认定死循环（这是投机取巧…..），经测试100即可AC。代码如下:

class Solution {public:    int getSSum(int n)    {        int rnt = 0;        while (n) {            int m = n % 10;            rnt += m * m;            n /= 10;        }        return rnt;    }    bool isHappy(int n) {        int ans = getSSum(n);        int times = 0,MAX = 100;        n = ans;        while (ans != 1 && times++ < MAX) {            ans = getSSum(n);            n = ans;        }        if (ans == 1)            return true;        else            return false;    }};