Happy Number

题目描述：

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 number12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

　　以前一直是按时间顺序做的，从这题开始按难易程度做。

我的解法：

bool isHappy(int n) {if(n <= 0)return false;set<int> st;while (1){int tmp = 0;while (n > 0){tmp += (n % 10)*(n % 10);n /= 10;}if(tmp == 1)return true;else{if(st.find(tmp) != st.end())return false;elsest.insert(tmp);}n = tmp;}
}

简洁版：

bool isHappy(int n) {if(n <= 0)return false;unordered_set<int> st;while (n != 1 && st.find(n) != st.end()){st.insert(n);int tmp = 0;do {tmp += (n % 10) * (n % 10);} while ( (n /= 10) > 0);n = tmp;}return n == 1;
}

转载于:https://www.cnblogs.com/gattaca/p/4594675.html

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Happy Number

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