Sliding Window - Minimum Consecutive Cards to Pick Up

Given an array of integers cards, return the minimum number of consecutive cards you have to pick up to have a pair of matching cards. If it is impossible, return -1.

Input: [3,4,2,3,4,7] → Output: 4

Input: [1,0,5,3] → Output: -1

Use a HashMap to track the last seen index of each card value. For each card, if seen before, the window size is current_index - last_index + 1. Track the minimum.

Maintain lastSeen HashMap.
For each index i: if lastSeen contains cards[i], compute window = i - lastSeen[cards[i]] + 1, update min.
Update lastSeen[cards[i]] = i.
Return min or -1 if no pair found.

import java.util.*; class Solution { public int minimumCardPickup(int[] cards) { Map<Integer, Integer> lastSeen = new HashMap<>(); int min = Integer.MAX_VALUE; for (int i = 0; i < cards.length; i++) { if (lastSeen.containsKey(cards[i])) min = Math.min(min, i - lastSeen.get(cards[i]) + 1); lastSeen.put(cards[i], i); } return min == Integer.MAX_VALUE ? -1 : min; } }

Time Complexity: O(N)
Space Complexity: O(N)