[LeetCode]Happy Number

標籤：

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

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

這道題要求判斷一個數是否是【幸福數】。
所謂幸福數，就是按照上述規則，依次求得數n各個位上的數位平方和，若該和等於1，則n是幸福數；如果不等於1，則將該和賦給n，繼續求平方和。直到判斷出結果。

需要注意的是，若一個數是幸福數，則必定會出現和為1的結果，可以跳出迴圈。而如果一個數不是幸福數，則可能一直迴圈下去。所以要找出跳出迴圈的條件：可以發現，當平方和等於不為1的一個數（0,2——9）時，就可以跳出迴圈，作出不是幸福數的判斷。

class Solution {public:   bool isHappy(int n) {        int ans = 0;        while (true){            while (n){                ans += pow(n % 10, 2);                n /= 10;            }            if (ans == 1)                return true;            else if (ans / 10 == 0)                return false;            else{                n = ans;                ans = 0;            }        }    }};

[LeetCode]Happy Number