Move pieces to obtain a string

Two Pointers String

56.7% acceptance

Feb 25, 2026

1460

You are given two strings start and target. Each consists of 'L', 'R', and '_'. 'L' can move left only if there is a blank to its left. 'R' can move right only if there is a blank to its right. Return true if it is possible to obtain target from start by moving pieces any number of times.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn can_change(start: String, target: String) -> bool {
    let s: Vec<char> = start.chars().collect();
    let t: Vec<char> = target.chars().collect();
    let pieces_s: Vec<(char, usize)> = s.iter().copied().enumerate()
      .filter(|(_, c)| *c != '_').map(|(i, c)| (c, i)).collect();
    let pieces_t: Vec<(char, usize)> = t.iter().copied().enumerate()
      .filter(|(_, c)| *c != '_').map(|(i, c)| (c, i)).collect();
    if pieces_s.len() != pieces_t.len() { return false; }
    for (ps, pt) in pieces_s.iter().zip(pieces_t.iter()) {
      if ps.0 != pt.0 { return false; }
      // L can only move left (to smaller index)
      if ps.0 == 'L' && ps.1 < pt.1 { return false; }
      // R can only move right (to larger index)
      if ps.0 == 'R' && ps.1 > pt.1 { return false; }
    }
    true
  }
}