[leetcode-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

思路：

类似于二分查找。

从0 和sqrt(n)两端分别查找。

bool judgeSquareSum(int c)
{
  if(c==0)return true;

  int qq = sqrt( (double)c );
    for( int ii= 0, pp = qq; ii<= qq && pp >= ii; )
    {
        int sum = ii * ii + pp * pp;
        if( sum < c )
            ii++;
        else if( sum > c )
            pp--;
        else
            return true;
      }

  return false;
}