HackerRank Lists Problem: Standard Test Case Works, But Others Don't - Python

Introduction

In this article, we will be discussing an issue faced by a programmer while solving a HackerRank problem related to lists in Python. The problem statement is easy to understand, but the solution implementation is quite tricky, especially if you are a beginner. The code works fine for the sample test case, but the code is failing some of the other test cases provided. In this article, we will be discussing the issue, its cause, and its solution.

Problem Statement

The problem statement is about implementing a list of commands that includes the following commands:

• "insert i e": Insert integer e at position i.
• "print": Print the list.
• "remove e": Delete the first occurrence of integer e.
• "append e": Insert integer e at the end of the list.
• "sort": Sort the list.
• "pop": Pop the last element from the list.
• "reverse": Reverse the list.

The program should take an integer input (N) followed by N command inputs. The program should then execute the list of commands and output the final list.

Sample Test Case

Let's take a look at a sample test case provided by HackerRank:

Sample Input 0:

12
insert 0 5
insert 1 10
insert 0 6
print
remove 6
append 9
append 1
sort
print
pop
reverse
print

Sample Output 0:

[6, 5, 10]
[1, 5, 9, 10]
[9, 5, 1]

Issue Faced by Programmer

The programmer was able to solve the problem and the sample test case was working fine, but some of the other test cases provided by HackerRank were failing. The issue was that the code was not able to execute the "print" command properly. It was supposed to print the list after executing all the commands, but the list was getting printed before executing all the commands. This was happening because of a newline character that was getting printed when the program was encountering the "print" command.

Solution

The solution to the issue is simple. We need to use the try and except block while executing the commands. We will be executing the commands by splitting the input command string using the split function. We will then use the first element of the split string as the command and the remaining elements as the arguments. For the "print" command, we will print the list only after executing all the other commands. Let's take a look at the updated code snippet below:

n = int(input())
lst = []

for _ in range(n):
    s = input()
    command = s.split()[0]
    args = s.split()[1:]
    
    try:
        if command == 'insert':
            lst.insert(int(args[0]), int(args[1]))

        elif command == 'print':
            print(lst)

        elif command == 'remove':
            lst.remove(int(args[0]))

        elif command == 'append':
            lst.append(int(args[0]))

        elif command == 'sort':
            lst.sort()

        elif command == 'pop':
            lst.pop()

        elif command == 'reverse':
            lst.reverse()
    except:
        print("Invalid command!")

print(lst)

We have added the try block around the if block where we are processing the commands. In the except block, we are printing "Invalid command!" if any invalid command is encountered. Also, we are only printing the list after executing all the commands.

Conclusion

In this article, we discussed an issue faced by a programmer while solving a HackerRank problem. We went through the problem statement, the issue faced, and its solution. We hope this article was helpful to you. Happy Coding!

References

[1] HackerRank, Lists