633. Sum of Square Numbers 平方数之和 看一个数是否能够有两个平方数组成

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

比较简单，开方求范围，然后使用左右指针

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