Find the most common response

Array Hash Table String Counting

75.0% acceptance

Feb 25, 2026

You are given a 2D string array responses where each responses[i] is an array of strings representing survey responses from the ith day. Return the most common response after removing duplicates within each day. If there is a tie, return the lexicographically smallest response.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn find_common_response(responses: Vec<Vec<String>>) -> String {
    use std::collections::{HashMap, HashSet};

    let mut freq: HashMap<String, usize> = HashMap::new();
    for day in &responses {
      let unique: HashSet<&String> = day.iter().collect();
      for s in unique {
        *freq.entry(s.clone()).or_insert(0) += 1;
      }
    }

    freq.into_iter()
      .max_by(|(ka, va), (kb, vb)| va.cmp(vb).then(kb.cmp(ka)))
      .map(|(k, _)| k)
      .unwrap_or_default()
  }
}