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Minimum Consecutive Cards to Pick Up

Difficulty: Medium

Problem Description

You are given an integer array cards where cards[i] represents the value of the i-th card. A pair of cards are matching if the cards have the same value. Return the minimum number of consecutive cards you have to pick up to have a pair of matching cards among the picked cards. If it is impossible to have matching cards, return -1.

Key Insights

  • We need to find the shortest subarray that contains at least one pair of matching cards.
  • Use a hash table (or dictionary) to track the last seen index of each card value.
  • The difference between the current index and the last seen index of a matching card gives the length of the consecutive cards needed.
  • The minimum length across all matching cards will give the result.

Space and Time Complexity

Time Complexity: O(n) - where n is the number of cards, as we traverse the array once. Space Complexity: O(n) - for the hash table storing the indices of the card values.

Solution

We will use a hash table to keep track of the last seen index of each card value. As we iterate through the cards, we will check if we have seen the card before. If we have, we calculate the length of the consecutive cards from the last seen index to the current index. We will keep track of the minimum length found. If no matching cards are found, we will return -1.

Code Solutions

def minimum_card_pickup(cards):
    last_seen = {}
    min_length = float('inf')
    
    for i, card in enumerate(cards):
        if card in last_seen:
            # Calculate the length of the consecutive cards
            length = i - last_seen[card] + 1
            min_length = min(min_length, length)
        # Update the last seen index for the card
        last_seen[card] = i
    
    return min_length if min_length != float('inf') else -1
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