Find occurrences of an element in an array

Array Hash Table

73.3% acceptance

Feb 24, 2026

181

You are given an integer array nums, an integer array queries, and an integer x. For each queries[i], you need to find the index of the queries[i]-th occurrence of x in the nums array. If there are fewer than queries[i] occurrences of x, the answer should be -1 for that query. Return an integer array answer containing the answers to all queries.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn occurrences_of_element(nums: Vec<i32>, queries: Vec<i32>, x: i32) -> Vec<i32> {
    let indices: Vec<i32> = nums
      .iter()
      .enumerate()
      .filter(|&(_, &v)| v == x)
      .map(|(i, _)| i as i32)
      .collect();
    queries
      .iter()
      .map(|&q| {
        let idx = (q - 1) as usize;
        if idx < indices.len() {
          indices[idx]
        } else {
          -1
        }
      })
      .collect()
  }
}