633. 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: 1 * 1 + 2 * 2 = 5
Example 2:
Input: 3
Output: False

这个题目认为完全平方数也应返回true, e.g. 4 = 0^2 + 2^2, 我第一次提交代码没有认为这一类也应包括在内．

class Solution {
public:
    bool judgeSquareSum(int c) {
        int up = sqrt(c);
        int left = 0, right = up;
        while(left <= right) {
            if(left * left + right * right == c) {
                return true;
            }
            else if(left * left + right* right < c) {
                left += 1;
            }
            else {
                right -= 1;
            }
        }
        
        return false;
    }
};