[LeetCode] 633. Sum of Square Numbers

题：https://leetcode.com/problems/sum-of-square-numbers/submissions/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.

Example 1:

Input: 5
Output: True
Explanation: 1 * 1 + 2 * 2 = 5

Example 2:

Input: 3
Output: False

思路

题目大意

给定一个数 c，c求 是否存在a，b使得a² + b² = c

解题思路

参考 Two Sum。pleft 指针为 0，pright为可能的最大值。求其平方的和 与 c比较，并相应移动两指针。

code

class Solution {
    public boolean judgeSquareSum(int c) {
        int i = 0,j = (int)Math.sqrt(c);
        while(i<=j){
            int tsum = i*i + j*j;
            if(tsum<c)  i++;
            else if(tsum>c) j--;
            else    return true;
        }
        return false;
    }
}