2657

2657. Find the Prefix Common Array of Two Arrays (Medium)

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.

Companies: Yandex

Related Topics:
Array, Hash Table

Solution 1.

// OJ: https://leetcode.com/problems/find-the-prefix-common-array-of-two-arrays
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    vector<int> findThePrefixCommonArray(vector<int>& A, vector<int>& B) {
        int N = A.size(), cnt = 0;
        vector<int> seen(N), ans(N);
        for (int i = 0; i < N; ++i) {
            if (++seen[A[i] - 1] == 2) ++cnt;
            if (++seen[B[i] - 1] == 2) ++cnt;
            ans[i] = cnt;
        }
        return ans;
    }
};