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
题目含义：给一个数字c，判断是否满足a平方+b平方=c
思路：a和b最大为c开根号，最小为0.

 1     public boolean judgeSquareSum(int c) {
 2         int a=0;
 3         int b=(int)Math.sqrt(c);
 4         while (a<=b)
 5         {
 6             double sum = a*a + b*b;
 7             if (sum ==c) return true;
 8             if (sum<c) a++;
 9             else b--;
10         }
11         return false;        
12     }