• [LeetCode] Happy Number


     

    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

    快乐数有以下的特性:在给定的进位制下,该数字所有数位(digits)的平方和,得到的新数再次求所有数位的平方和,如此重复进行,最终结果必为1。

    非快乐数有以下的特性:所有不快乐数的数位平方和计算,最後都会进入 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20 → 4 的循环中。

    所以外层循环:判断是否为快乐数和非快乐数。内层循环对n进行快乐数分解计算。

    class Solution {
    public:
        bool isHappy(int n) {
            while (n != 1 && n != 4) {
                int sum = 0, tmp = 0;
                while (n != 0) {
                    tmp = n % 10;
                    sum += tmp * tmp;
                    n /= 10;
                }
                n = sum;
            }
            return n == 1;
        }
    };
    // 3 ms
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  • 原文地址:https://www.cnblogs.com/immjc/p/7219090.html
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