Maximum number of pairs in array

Array Hash Table Counting

76.0% acceptance

Feb 25, 2026

740

You are given a 0-indexed integer array nums. In one operation, you may do the following: Choose two integers in nums that are equal. Remove both integers from nums, forming a pair. The operation is done on nums as many times as possible. Return a 0-indexed integer array answer of size 2 where answer[0] is the number of pairs that are formed and answer[1] is the number of leftover integers in nums after doing the operation as many times as possible.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn number_of_pairs(nums: Vec<i32>) -> Vec<i32> {
    let mut freq = [0i32; 101];
    for &n in &nums { freq[n as usize] += 1; }
    let pairs: i32 = freq.iter().map(|&f| f / 2).sum();
    let leftover: i32 = freq.iter().map(|&f| f % 2).sum();
    vec![pairs, leftover]
  }
}