Largest time for given digits

Array String Backtracking Enumeration

35.8% acceptance

Feb 25, 2026

745

1072

Given an array arr of 4 digits, find the latest 24-hour time that can be made using each digit exactly once. 24-hour times are formatted as "HH:MM", where HH is between 00 and 23, and MM is between 00 and 59. The earliest 24-hour time is 00:00, and the latest is 23:59. Return the latest 24-hour time in "HH:MM" format. If no valid time can be made, return an empty string.

Solution

Rust

Time O(n³)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn largest_time_from_digits(arr: Vec<i32>) -> String {
    let mut best = -1i32;
    let _digits = [0,1,2,3];
    // Try all permutations of indices
    for a in 0..4 {
      for b in 0..4 {
        if b == a { continue; }
        for c in 0..4 {
          if c == a || c == b { continue; }
          let d = 6 - a - b - c; // remaining index
          let h = arr[a]*10 + arr[b];
          let m = arr[c]*10 + arr[d];
          if h < 24 && m < 60 {
            let t = h * 60 + m;
            if t > best { best = t; }
          }
        }
      }
    }
    if best == -1 { return "".to_string(); }
    format!("{:02}:{:02}", best / 60, best % 60)
  }
}