1346. Check If N and Its Double Exist

Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).

More formally check if there exists two indices i and j such that :

  • i != j
  • 0 <= i, j < arr.length
  • arr[i] == 2 * arr[j]

 

Example 1:

Input: arr = [10,2,5,3]
Output: true
Explanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.

Example 2:

Input: arr = [7,1,14,11]
Output: true
Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.

Example 3:

Input: arr = [3,1,7,11]
Output: false
Explanation: In this case does not exist N and M, such that N = 2 * M.

 

Constraints:

  • 2 <= arr.length <= 500
  • -10^3 <= arr[i] <= 10^3

Rust Solution

struct Solution;
use std::collections::HashSet;

impl Solution {
    fn check_if_exist(arr: Vec<i32>) -> bool {
        let mut hs: HashSet<i32> = HashSet::new();
        let mut zero = 0;
        for &x in &arr {
            if x == 0 {
                if zero > 0 {
                    return true;
                } else {
                    zero += 1;
                }
            } else {
                hs.insert(x);
            }
        }
        for x in arr {
            if hs.contains(&(2 * x)) {
                return true;
            }
        }
        false
    }
}

#[test]
fn test() {
    let arr = vec![10, 2, 5, 3];
    let res = true;
    assert_eq!(Solution::check_if_exist(arr), res);
    let arr = vec![7, 1, 14, 11];
    let res = true;
    assert_eq!(Solution::check_if_exist(arr), res);
    let arr = vec![3, 1, 7, 11];
    let res = false;
    assert_eq!(Solution::check_if_exist(arr), res);
    let arr = vec![-2, 0, 10, -19, 4, 6, -8];
    let res = false;
    assert_eq!(Solution::check_if_exist(arr), res);
}

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