202. 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

思路：

采用set来判断容器中是否有该元素出现过，如果出现过，那么就形成了环状，结果返回false。否则找到快乐数字。返回true。

代码如下：

class Solution {
public:
    bool isHappy(int n) {
        set<int > myset;
        int total = 0;
        while(n != 1)
        {
            while(n)
            {
                total += (n%10)*(n%10);
                n /= 10;
            }
            if(total == 1)
                return true;
            if(myset.find(total) != myset.end())
                return false;
            else
                myset.insert(total);
            n = total;
            total = 0;
        }
        return true;
    }
};

关于set容器的使用练习。

2016-08-13 13:49:32