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
Credits:
Special thanks to @mithmatt and @ts for
adding this problem and creating all test cases.
Subscribe to see which companies asked this question
由于不知道如何判断一个数不是happy数（如果是就简单了），学习和参考了别人家的解法：
class Solution {
public:
int getSquare(int num){ //because square operation is very often, so enum the result
switch(num){
case 0: return 0;
case 1: return 1;
case 2: return 4;
case 3: return 9;
case 4: return 16;
case 5: return 25;
case 6: return 36;
case 7: return 49;
case 8: return 64;
case 9: return 81;
}
}
bool isHappy(int n) {
if(n == 0) return false;
set<int> squareSum;
return dfs(n, squareSum);
}
bool dfs(int n, set<int>& squareSum){
int tmp;
int sum = 0;
while(n){
tmp = n%10;
sum += getSquare(tmp);
n /= 10;
}
if(sum == 1) return true;
else if(squareSum.find(sum)!=squareSum.end()) return false;
else {
squareSum.insert(sum);
return dfs(sum, squareSum);
}
}
};参考资源：
【1】 博文地址，http://www.cnblogs.com/qionglouyuyu/p/5052927.html
<LeetCode OJ> Happy Number【202】
原文：http://blog.csdn.net/ebowtang/article/details/50417558