LeetCode 1640: Check Array Formation Through Concatenation

Explanation

To solve this problem, we need to check if it is possible to form the array arr by concatenating the arrays in pieces without reordering the integers within each array in pieces. We can achieve this by mapping each integer in arr to its corresponding piece in pieces and checking if the concatenation of these mapped pieces matches the original arr.

We can create a mapping of the first integer of each piece to the entire piece. Then, we iterate through arr, check if the integer is in our mapping, and concatenate the corresponding piece. If at any point we encounter an integer that is not in the mapping or the final concatenated array does not match arr, we return false.

class Solution {
    public boolean canFormArray(int[] arr, int[][] pieces) {
        Map<Integer, int[]> map = new HashMap<>();
        for (int[] piece : pieces) {
            map.put(piece[0], piece);
        }
        
        int[] result = new int[arr.length];
        int idx = 0;
        for (int num : arr) {
            if (map.containsKey(num)) {
                int[] piece = map.get(num);
                for (int i = 0; i < piece.length; i++) {
                    result[idx++] = piece[i];
                }
            } else {
                return false;
            }
        }
        
        return Arrays.equals(arr, result);
    }
}