lintcode: Check Sum of Square Numbers

Check Sum of Square Numbers 

Given a integer c, your task is to decide whether there're two integers a and b such that a^2 + b^2 = c.

您在真实的面试中是否遇到过这个题？ 

Yes

样例

Given n = 5
Return true // 1 * 1 + 2 * 2 = 5

Given n = -5
Return false

代码

class Solution {
public:
    /*
     * @param : the given number
     * @return: whether whether there're two integers
     */
    bool checkSumOfSquareNumbers(int num) {
        // write your code here
        if (num < 0) {
            return false;
        }
        int c = floor(sqrt(num));
        int i = c;
        if (i * i == num) return true;
        int j = 1;
        while (j <= i) {
            if (i * i + j * j == num) {
                return true;
            } else if (i * i + j * j < num) {
                j++;
            } else {
                i--;
            }
        }
        return false;
    }
};