2657. Find the Prefix Common Array of Two Arrays

MediumView on LeetCode

Array Hash Table Bit Manipulation Prefix Sum

Time: O(n)

Space: O(n)

Intuition

Find the k closest numbers using a two-pointer approach on sorted array or priority queue.

Algorithm

1Sort. Binary search for insertion point of target. Two pointers expanding outward. Take k closest.

Common Pitfalls

•Tie-breaking: prefer smaller element. Two pointers from found position outward.

2657.cs

// Approach: Track seen elements from A and B using sets; count overlap at each index.
// Time: O(n) Space: O(n)

public class Solution
{
    public int[] FindThePrefixCommonArray(int[] A, int[] B)
    {
        int[] commonArray = new int[A.Length];
        int commonNos = 0;
        for (int i = 0; i < A.Length; i++)
        {
            commonNos = 0;
            for (int j = 0; j <= i; j++)
            {
                for (int k = 0; k <= i; k++)
                {
                    if (A[j] == B[k])
                    {
                        commonNos++;
                    }
                }
            }
            Console.WriteLine("Common numbers: " + commonNos);
            commonArray[i] = commonNos;
        }

        return commonArray;
    }
}

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