Sum of Square Numbers

Given a non-negative integer c, your task is to decide whether there're two integers a and b such that a² + b² = c.

Example 1:
Input: 5
Output: true
Explanation:1² + 2² = 5

Example 2:
Input: 3
Output: false

Source:LeetCode

Solution in C++

The idea is simple: Instead of looking for all possible combinations of a and b. Iterate from 0 to sqrt(c), check if the result of c - a² is a perfect square, if so,we have found the combinations of sum of squares (a² + b² = c).
 

class Solution {
public:
    bool judgeSquareSum(int c) {   
        for(int i=0;i<=(int)sqrt(c);++i)
            if(is_perfect_square(c-i*i))  //check is the number is perfect square
                return true;
        
        return false;
    }
    bool is_perfect_square(int num){
        int sq = sqrt(num);
        return sq*sq == num;
    }
    
};