Matchsticks to square

Array Dynamic Programming Backtracking Bit Manipulation Bitmask

41.6% acceptance

Jan 13, 2026

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You are given an integer array matchsticks where matchsticks[i] is the length of the ith matchstick. You want to use all the matchsticks to make one square. You should not break any stick, but you can link them up, and each matchstick must be used exactly one time. Return true if you can make this square and false otherwise.

Solution

Rust

Time O(n log n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn makesquare(mut matchsticks: Vec<i32>) -> bool {
    let sum: i32 = matchsticks.iter().sum();
    if sum % 4 != 0 { return false; }
    let target = sum / 4;
    matchsticks.sort_by(|a, b| b.cmp(a));
    let mut sides = vec![0; 4];
    Self::dfs(&matchsticks, 0, &mut sides, target)
  }
  
  fn dfs(sticks: &[i32], idx: usize, sides: &mut Vec<i32>, target: i32) -> bool {
    if idx == sticks.len() {
      return sides.iter().all(|&s| s == target);
    }
    for i in 0..4 {
      if sides[i] + sticks[idx] <= target {
        sides[i] += sticks[idx];
        if Self::dfs(sticks, idx + 1, sides, target) { return true; }
        sides[i] -= sticks[idx];
      }
      if sides[i] == 0 { break; }
    }
    false
  }
}