Find Anagram Mappings

Given two lists A and B, and B is an anagram of A. B is an anagram of A means B is made by randomizing the order of the elements in A. We want to find an index mapping P, from A to B. A mapping P[i] = j means the ith element in A appears in B at index j. These lists A and B may contain duplicates. If there are multiple answers, output any of them.

• A, B have equal lengths in range [1, 100].

• A[i], B[i] are integers in range [0, 10^5].

Example

Example1

Input:  A = [12, 28, 46, 32, 50] and B = [50, 12, 32, 46, 28]
Output: [1, 4, 3, 2, 0]
Explanation:
As P[0] = 1 because the 0th element of A appears at B[1], and P[1] = 4 because the 1st element of A appears at B[4], and so on.

Example2

Input:  A = [1, 2, 3, 4, 5] and B = [5, 4, 3, 2, 1]
Output: [4, 3, 2, 1, 0]
Explanation:
As P[0] = 4 because the 0th element of A appears at B[4], and P[1] = 3 because the 1st element of A appears at B[3], and so on.

public class Solution {
    // O(n) time & O(n) Space
    public int[] anagramMappings(int[] A, int[] B) {
        int[] ans = new int[A.length];
        Map<Integer, List<Integer>> map = new HashMap<>();
        for (int j = 0; j < B.length; j++)
            map.computeIfAbsent(B[j], k -> new ArrayList<>()).add(j);
        for (int i = 0; i < A.length; i++) {
            int size = map.get(A[i]).size();
            ans[i] = map.get(A[i]).get(size - 1);
            map.get(A[i]).remove(size - 1);
        }
        return ans;
    }
}