README.md

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

Solutions (Rust)

1. HashMap

use std::collections::HashSet;

impl Solution {
    pub fn judge_square_sum(c: i32) -> bool {
        let mut b2 = HashSet::new();
        let mut a = 0_i32;

        while let Some(a2) = a.checked_mul(a) {
            if a2 > c {
                break;
            }

            b2.insert(a2);

            if b2.contains(&(c - a2)) {
                return true;
            }

            a += 1;
        }

        false
    }
}

2. Two Pointers

impl Solution {
    pub fn judge_square_sum(c: i32) -> bool {
        let mut a = 0;
        let mut b = c.min(46340);

        while a <= b {
            if c - b * b > a * a {
                a += 1;
            } else if c - b * b < a * a {
                b -= 1;
            } else {
                return true;
            }
        }

        false
    }
}