15算法课程 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 = 828² + 2² = 686² + 8² = 1001² + 0² + 0² = 1

solution:

哈希记录出现的次数防止出现循环

code:

class Solution { public: bool isHappy(int n) { unordered_map<int,bool> mp; mp[n] = true; while(n!=1){ int sum = 0 ; do{ int remain = n; sum += remain*remain; n/=10; }while(n!=0); if(mp[sum]) return false; mp[sum] = true; n = sum; } return true; } };