Minimum Consecutive Cards to Pick up solution leetcode

An interesting problem on leetcode to find minimum number of ways to pick up consecutive cards. We will start with a brute force algorithm that would exceed in time limit. Later we will improve upon this algorithm using hashmap.

Problem Statement

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.

Brute force Solution

A simple intuitive solution would be to pick up a card, and then iterate over the remaining cards to find the minimum length.

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Python

This will fail as the time limit will exceed while submiting the solution to leetcode. This is because the time complexity of the solution is O(n²).

Using HashMap

Lets take an example with a use case of following input

cards = [3,4,2,3,4,7]

Next we can create a hashmap to keep track of indices of a particular card.

Java
Python

Complexity

Time Complexity is $$\theta(n * m)$$.