LeetCode——Happy Number

题目：
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

解答：

class Solution {public:    bool isHappy(int n) {        if (n <= 0) {            return false;        }        set<int> numSet;        const int kMaxDigitNum = 11;        const int kUnInitValue = -1;        vector<int> digits(kMaxDigitNum, kUnInitValue);        int cur = n;        while(numSet.find(cur) == numSet.end()) {            numSet.insert(cur);            int i = 0;            while (cur > 0) {                int digit = cur % 10;                if (digit) {                   digits[i++] = digit;                }                cur /= 10;            }            if (digits[0] == 1 && digits[1] == kUnInitValue) {                return true;            }            int j = 0;            while (digits[j] != kUnInitValue) {                cur += digits[j] * digits[j];                ++j;            }            for (int k = 0; k != kMaxDigitNum; ++k) {                digits[k] = kUnInitValue;            }        }        return false;    }};