LeetCode OJ：Happy Number（欢乐数）

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

• 1 + 81 = 82
• 64 + 4 = 68
• 36 + 64 = 100
• 1 + 0 + 0 = 1

欢乐数，就是不断将位的平方相加为新数，看看最后得到的数是不是1，是的话就是欢乐数，否则不是。代码比较简单，用一个set保存下来已经求到过的不是1的数字，一旦

后期某个计算到的数字能在set中找到（不是1），那么就一定进入到死循环当中了。这是就应该返回false， 否则一旦某个计算结果是1那么久返回true，代码见下：

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

 java版本如下所示，方法相同：

public class Solution {
    public boolean isHappy(int n) {
        HashSet<Integer> set = new HashSet<Integer>();
        do{
            if(set.contains(n))
                return false;
            set.add(n);
            int tmp = 0;
            while(n != 0){
                tmp += (n%10)*(n%10);
                n/=10;
            }
            n = tmp;
        }while(n!=1);
        return true;
    }
}