Find all duplicates in an array

Array Hash Table Sorting

76.8% acceptance

Jan 13, 2026

11110

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Given an integer array nums of length n where all the integers of nums are in the range [1, n] and each integer appears at most twice, return an array of all the integers that appears twice. You must write an algorithm that runs in O(n) time and uses only constant auxiliary space, excluding the space needed to store the output

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn find_duplicates(mut nums: Vec<i32>) -> Vec<i32> {
    let mut result = Vec::new();
    
    for i in 0..nums.len() {
      let idx = (nums[i].abs() - 1) as usize;
      if nums[idx] < 0 {
        result.push(nums[i].abs());
      } else {
        nums[idx] = -nums[idx];
      }
    }
    
    result
  }
}