2657 - Find the Prefix Common Array of Two Arrays

Description (leetcode)

You are given two 0-indexedintegerpermutations 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 ofAandB.

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.

submission

use std::collections::HashSet;

impl Solution {
    pub fn find_the_prefix_common_array(a: Vec<i32>, b: Vec<i32>) -> Vec<i32> {
        a.into_iter()
            .zip(b)
            .scan((HashSet::new(), HashSet::new()), |(ca, cb), (va, vb)| {
                ca.insert(va);
                cb.insert(vb);
                Some(ca.intersection(&cb).count() as i32)
            })
            .collect()
    }
}