Leaderboard implementation in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Retrieve top 3 players from leaderboard

Given a Redis sorted set game_leaderboard where player scores are stored, which command returns the top 3 players with the highest scores?

Redis

ZADD game_leaderboard 1500 player1 1800 player2 1200 player3 2000 player4 1700 player5

A ZREVRANGE game_leaderboard 0 2 WITHSCORES

B ZRANGEBYSCORE game_leaderboard 0 3 WITHSCORES

C ZRANGE game_leaderboard 0 2 WITHSCORES

D ZREVRANGEBYSCORE game_leaderboard 0 3 WITHSCORES

💡 Hint

Remember that higher scores mean higher rank, and ZREVRANGE returns elements from highest to lowest score.

ZREVRANGE returns elements in descending order of score. Using 0 2 gets the top 3 players. WITHSCORES includes their scores in the output.

🧠 Conceptual

intermediate

Understanding score updates in Redis leaderboard

Which Redis command correctly increases the score of player3 by 300 points in the game_leaderboard sorted set?

A ZADD game_leaderboard player3 300

B ZADD game_leaderboard 300 player3

C ZINCRBY player3 300 game_leaderboard

D ZINCRBY game_leaderboard 300 player3

💡 Hint

Look for the command that increments a member's score by a given amount.

ZINCRBY increments the score of a member in a sorted set by the specified amount. The syntax is ZINCRBY key increment member.

📝 Syntax

advanced

Identify the syntax error in leaderboard score retrieval

Which option contains a syntax error when trying to get the rank of player2 in game_leaderboard?

A ZRANK game_leaderboard player2

B ZREVRANK game_leaderboard player2

C ZRANK player2 game_leaderboard

D 2reyalp draobredael_emag KNARVERZ

💡 Hint

Check the order of arguments for the rank commands.

ZRANK and ZREVRANK require the sorted set key first, then the member. Option C reverses this order, causing a syntax error.

❓ optimization

advanced

Efficiently retrieve players ranked 5 to 10 with scores

Which Redis command efficiently retrieves players ranked from 5 to 10 (inclusive) with their scores from game_leaderboard, sorted from highest to lowest score?

A ZREVRANGE game_leaderboard 4 9 WITHSCORES

B ZREVRANGEBYSCORE game_leaderboard 10 5 WITHSCORES

C ZRANGEBYSCORE game_leaderboard 5 10 WITHSCORES

D ZRANGE game_leaderboard 4 9 WITHSCORES

💡 Hint

Remember that ranks start at 0 and ZREVRANGE returns highest scores first.

Ranks start at 0, so rank 5 is index 4. ZREVRANGE returns members from highest to lowest score. Using 4 9 gets ranks 5 to 10.

🔧 Debug

expert

Why does this leaderboard update fail?

Consider this Redis command intended to update player6's score to 2500 in game_leaderboard:

ZINCRBY game_leaderboard 2500 player6

Why might this command not set player6's score to exactly 2500?

A Because <code>ZINCRBY</code> requires the member name before the increment value

B Because <code>ZINCRBY</code> adds 2500 to the existing score instead of setting it directly

C Because <code>ZINCRBY</code> only works if the member already exists

D Because <code>ZINCRBY</code> cannot be used on sorted sets

💡 Hint

Think about what ZINCRBY does to the score value.

ZINCRBY increases the current score by the given increment. It does not set the score to that value. To set a score directly, use ZADD with the new score.