leetcode 633. Sum of Square Numbers

1.题目

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

给一个数字C，判断C是否能由两个数的平方组成

Example 1:

Input: 5

Output: True

Explanation: 1 * 1 + 2 * 2 = 5

Example 2:

Input: 3

Output: False

2.分析

要找出是否存在a2 + b2 = c. 先限定a,b的范围。 0<=a,b<=sqrt(c)

然后从两端向中间逼近。

3.代码

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