Check array formation through concatenation

Array Hash Table

57.3% acceptance

Feb 25, 2026

940

143

You are given an array of distinct integers arr and an array of integer arrays pieces, where the integers in pieces are distinct. Your goal is to form arr by concatenating the arrays in pieces in any order. However, you are not allowed to reorder the integers in each array pieces[i]. Return true if it is possible to form the array arr from pieces. Otherwise, return false.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

use std::collections::HashMap;

impl Solution {
  pub fn can_form_array(arr: Vec<i32>, pieces: Vec<Vec<i32>>) -> bool {
    let map: HashMap<i32, &Vec<i32>> = pieces.iter().map(|p| (p[0], p)).collect();
    let mut i = 0;
    while i < arr.len() {
      if let Some(piece) = map.get(&arr[i]) {
        if arr[i..i+piece.len()] == piece[..] {
          i += piece.len();
        } else {
          return false;
        }
      } else {
        return false;
      }
    }
    true
  }
}