2657. Find the Prefix Common Array of Two Arrays

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2657. Find the Prefix Common Array of Two Arrays

Description

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 apermutation if it contains all integers from 1 to n exactly once.

Example 1:

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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:

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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.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    vector<int> findThePrefixCommonArray(vector<int>& A, vector<int>& B) {
        long long a = 0, b = 0;
        vector<int> res;
        int n = A.size();
        for (int i = 0; i < n; i++) {
            a |= (1LL << (A[i]));
            b |= (1LL << (B[i]));
            int num = __builtin_popcountll(a & b);
            res.push_back(num);
        }
        return res;
    }
};