202. Happy Number (INT)

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

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);
        }
    }
};