2657.FindThePrefixCommonArrayOfTwoArrays.md

2657. Find the Prefix Common Array of Two Arrays

LeetCode Problem Link

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.

Solution

JavaScript

/**
 * @param {number[]} A
 * @param {number[]} B
 * @return {number[]}
 */
var findThePrefixCommonArray = function(A, B) {
    const n = A.length;
    let prefixCommon = 0
    const result = Array(n).fill(0);
    const count = Array(n+1).fill(0);
    for(let i = 0; i < n; i++){
        if(++count[A[i]] == 2){
            ++prefixCommon;
        }

        if(++count[B[i]] == 2){
            ++prefixCommon;
        }

        result[i] = prefixCommon;
    }
    return result;
};