LeetCode 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 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

The original problem is here.

The original code is here.

My Solution

I solve this problem in C++, as below:

*Happy Number
*Author: shuaijiang
*Email: zhaoshuaijiang8@gmail.com
using namespace std;

class Solution {
    bool isHappy(int n) {
        map<int,int> myMap;
        myMap[n] = 1;
            n = squareSum(n);
            if(n == 1)
                myMap[n] = 1;
                return false;
        return true;
    int squareSum(int n){
        vector<int> vec;
        int elem = 0, sum = 0;
            elem = n % 10;
            n = n / 10;
        for(int count=0;count<vec.size();++count){
            sum += vec[count] * vec[count];
        return sum;


To solve the problem, we should compute the square sum of each digits of the number. It is important that when to finish the procedure of computation of the square sum. I use a hash(map in C++) to save the sum computed before, and when a new sum come, if we can get it from the hash, then we know that a circle exists, and the number is not a happy number. However, if the sum is equal to 1, then it is a happy number.