Minimum number of keypresses

Hash Table String Greedy Sorting Counting

71.5% acceptance

Mar 31, 2026

250

You have a keypad with 9 buttons, numbered from 1 to 9, each mapped to lowercase English letters. You can choose which characters each button is matched to as long as: All 26 lowercase English letters are mapped to. Each character is mapped to by exactly 1 button. Each button maps to at most 3 characters. To type the first character matched to a button, you press the button once. To type the second character, you press the button twice, and so on. Given a string s, return the minimum number of keypresses needed to type s using your keypad. Note that the characters mapped to by each button, and the order they are mapped in cannot be changed.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn minimum_keypresses(s: String) -> i32 {
    let mut freq = [0i32; 26];
    for b in s.bytes() {
      freq[(b - b'a') as usize] += 1;
    }
    freq.sort_unstable_by(|a, b| b.cmp(a));
    let mut total = 0;
    for (i, &f) in freq.iter().enumerate() {
      if f == 0 { break; }
      total += f * (i as i32 / 9 + 1);
    }
    total
  }
}