633.平方数之和

class Solution {
public:
    bool judgeSquareSum(int c) {
        long i = 0, j = sqrt(c);
        while (i <= j) 
            if (i * i + j * j == c) return true;
            else if (i * i + j * j > c) j --;
            else i ++;
        return false;
    }
};