Resolving heap-buffer-overflow Issues in LeetCode's strStr Problem

Dive into the details of fixing the `heap-buffer-overflow` error encountered in LeetCode's `strStr` problem with a clearer approach and improved code examples.
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Troubleshooting heap-buffer-overflow in LeetCode's strStr Problem

When tackling coding problems on platforms like LeetCode, you may occasionally encounter errors that leave you scratching your head—like the dreaded heap-buffer-overflow. A common scenario is when trying to implement the strStr function in C, leading to unexpected behaviors. This guide will break down the issue and guide you through a solution that avoids these pitfalls.

Understanding the Problem

The strStr function is designed to find the first occurrence of a substring (needle) within a string (haystack). The challenge lies in handling edge cases and ensuring that we don't read beyond the bounds of our allocated memory, which can cause a heap-buffer-overflow. In this case, the implementation that worked locally caused issues when submitted on LeetCode.

Original Code and Error

The original code might look something like this:

[[See Video to Reveal this Text or Code Snippet]]

The error message indicated a problem with memory access, caused by incrementing i in the inner loop and again in the outer loop, potentially skipping the null terminator at the end of haystack. This leads to accessing memory beyond the allocated space.

Revising the Solution

Here’s a revised version of the function, correcting the mistake and ensuring safe memory access while still achieving the desired functionality:

Improved Code

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made

Index Management: The inner loop now increments j while checking haystack[i + j] against needle[j]. This ensures we are always checking the correct characters relative to i, safeguarding against accessing out-of-bounds memory.

Simplification: This version reduces redundancy and enhances readability.

Considering Performance

Although this approach is straightforward, keep in mind the time complexity can be worst-case O(len(haystack) * len(needle)). A pathological scenario would be:

[[See Video to Reveal this Text or Code Snippet]]

This showcases how performance can degrade with certain inputs, which is essential to consider for larger datasets.

Conclusion

By understanding and addressing the underlying causes of the heap-buffer-overflow error in the strStr function, you can write safer, more efficient code that passes the constraints on platforms like LeetCode. Happy coding!