Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 14

Description

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.

Solution

class Solution {
public:
  vector<int> findThePrefixCommonArray(vector<int>& A, vector<int>& B) {
    int len = A.size();
    set<int> a, b;
    vector<int> answer;
    answer.reserve(len);
    A.reserve(len);
    B.reserve(len);
    int count = 0;
    for(int i = 0; i < A.size(); ++i) {
      a.insert(A[i]);
      b.insert(B[i]);
      count += a.count(B[i]) + b.count(A[i]) - (A[i] == B[i]);
      answer.push_back(count);
    }
    return answer;
  }
};

// Accepted
// 1773/1773 cases passed (14 ms)
// Your runtime beats 35.21 % of cpp submissions
// Your memory usage beats 11.23 % of cpp submissions (91.1 MB)