last_seen to store the last seen index of each card value.min_length to store the minimum length of a sequence with a matching pair, set it to a large value initially.cards array with index i.
a. If the current card value cards[i] is in last_seen, calculate the length of the sequence as i - last_seen[cards[i]] + 1.
b. If the calculated length is less than min_length, update min_length.
c. Update last_seen[cards[i]] with the current index i.min_length is still the initial large value, return -1, indicating no matching pairs were found.min_length as the result.