Adding spaces to a string

Array Two Pointers String Simulation

71.8% acceptance

Feb 25, 2026

1116

113

You are given a 0-indexed string s and a 0-indexed integer array spaces that describes the indices in the original string where spaces will be added. Each space should be inserted before the character at the given index. For example, given s = "EnjoyYourCoffee" and spaces = [5, 9], we place spaces before 'Y' and 'C', which are at indices 5 and 9 respectively. Thus, we obtain "Enjoy Your Coffee". Return the modified string after the spaces have been added.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn add_spaces(s: String, spaces: Vec<i32>) -> String {
    let s = s.as_bytes();
    let mut result = Vec::with_capacity(s.len() + spaces.len());
    let mut sp_idx = 0;
    for (i, &c) in s.iter().enumerate() {
      if sp_idx < spaces.len() && spaces[sp_idx] == i as i32 {
        result.push(b' ');
        sp_idx += 1;
      }
      result.push(c);
    }
    String::from_utf8(result).unwrap()
  }
}