README.md

2007. Find Original Array From Doubled Array

An integer array original is transformed into a doubled array changed by appending twice the value of every element in original, and then randomly shuffling the resulting array.

Given an array changed, return original if changed is a doubled array. If changed is not a doubled array, return an empty array. The elements in original may be returned in any order.

Example 1:

Input: changed = [1,3,4,2,6,8]
Output: [1,3,4]
Explanation: One possible original array could be [1,3,4]:
- Twice the value of 1 is 1 * 2 = 2.
- Twice the value of 3 is 3 * 2 = 6.
- Twice the value of 4 is 4 * 2 = 8.
Other original arrays could be [4,3,1] or [3,1,4].

Example 2:

Input: changed = [6,3,0,1]
Output: []
Explanation: changed is not a doubled array.

Example 3:

Input: changed = [1]
Output: []
Explanation: changed is not a doubled array.

Constraints:

• 1 <= changed.length <= 105
• 0 <= changed[i] <= 105

Solutions (Rust)

1. Solution

use std::collections::HashMap;

impl Solution {
    pub fn find_original_array(changed: Vec<i32>) -> Vec<i32> {
        let mut changed = changed;
        let mut count = HashMap::new();
        let mut original = vec![];

        changed.sort_unstable();

        for num in &changed {
            if num % 2 == 0 && *count.get(&(num / 2)).unwrap_or(&0) > 0 {
                *count.get_mut(&(num / 2)).unwrap() -= 1;
                original.push(num / 2);
            } else {
                *count.entry(num).or_insert(0) += 1;
            }
        }

        if original.len() * 2 != changed.len() {
            original.clear();
        }

        original
    }
}