Find the Prefix Common Array of Two Arrays

# 2657. Find the Prefix Common Array of Two Arrays

You are given two 0-indexed integer permutations A and B of length n.

A prefix common array of A and B is an array C such that C[i] is equal to the count of numbers that are present at or before the index i in both A and B.

Return the prefix common array of A and B.

A sequence of n integers is called a permutation if it contains all integers from 1 to n exactly once.

### Example 1:
```
Input: A = [1,3,2,4], B = [3,1,2,4]
Output: [0,2,3,4]
Explanation: At i = 0: no number is common, so C[0] = 0.
At i = 1: 1 and 3 are common in A and B, so C[1] = 2.
At i = 2: 1, 2, and 3 are common in A and B, so C[2] = 3.
At i = 3: 1, 2, 3, and 4 are common in A and B, so C[3] = 4.
```

### Example 2:
```
Input: A = [2,3,1], B = [3,1,2]
Output: [0,1,3]
Explanation: At i = 0: no number is common, so C[0] = 0.
At i = 1: only 3 is common in A and B, so C[1] = 1.
At i = 2: 1, 2, and 3 are common in A and B, so C[2] = 3.
 ```

Constraints:
```
1 <= A.length == B.length == n <= 50
1 <= A[i], B[i] <= n
It is guaranteed that A and B are both a permutation of n integers.
```

/**
 * @param {number[]} A
 * @param {number[]} B
 * @return {number[]}
 */
const findThePrefixCommonArray = function(A, B) {
    const aSet = new Set(), bSet = new Set(), usedSet = new Set(), out = [];
    let count = 0;

    const markAsUsed = (element, setObj) => {
        if (setObj.has(element) && !usedSet.has(element)) {
            count++;
            usedSet.add(element);
        }
    }
    A.forEach((elementA, index) => {
        markAsUsed(A[index], bSet.add(B[index]));
        markAsUsed(B[index], aSet.add(A[index]));
        out.push(count);
    })
    return out;
};