Sum of Square Numbers

题目
Given a non-negative integer c, your task is to decide whether there're two integers a and b such that a^2 + b^2 = c.

答案

class Solution {
    public boolean judgeSquareSum(int c) {
        Set<Integer> set = new HashSet<>();
        for(int i = 0; i <= Math.sqrt(c); i++) {
            set.add(i*i);
            if(set.contains(c - i*i)) return true;
        }
        return false;
    }
}

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