Largest 3 same digit number in string

String

72.7% acceptance

Feb 25, 2026

1388

You are given a string num representing a large integer. An integer is good if it meets the following conditions: It is a substring of num with length 3. It consists of only one unique digit. Return the maximum good integer as a string or an empty string "" if no such integer exists. Note: A substring is a contiguous sequence of characters within a string. There may be leading zeroes in num or a good integer.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn largest_good_integer(num: String) -> String {
    let bytes = num.as_bytes();
    let mut best: Option<u8> = None;
    for i in 0..bytes.len()-2 {
      if bytes[i] == bytes[i+1] && bytes[i+1] == bytes[i+2] {
        let d = bytes[i];
        if best.map_or(true, |b| d > b) {
          best = Some(d);
        }
      }
    }
    best.map_or(String::new(), |d| {
      let ch = d as char;
      format!("{}{}{}", ch, ch, ch)
    })
  }
}