Leetcode Solutions

Merge two sorted lists

problems faced:

1. Error: Line 90: Char 22: runtime error: member access within misaligned address 0x00000000001f for type 'const ListNode', which requires 8 byte alignment (_Serializer_.cpp) 0x00000000001f: note: pointer points here SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior _Serializer_.cpp:99:22
2. Realized that my current3 pointer wasn’t getting updated when I used a function to create new ListNodes dynamically.
3. This is probably because my function was creating a copy of the pointer variables I passed in the argument. Don’t confuse it with when we pass stuff by reference. When we used to apply functions to arrays(say) by passing pointers to it, we usually had to edit the information on the address that the pointer contained and not the address itself, which is why we didn’t come across any problems. Here, however, we need to modify the value in the pointer itself, and so we should pass a reference to the pointer variable in the function.
4. Edit: the code DOES work. It’s just that since I was calling it in the main function, the memory pertaining to the first ListNode of list3, which resided in the stack and not the heap, was getting freed, making it impossible to access other nodes. Adding a for loop to the function itself, the code prints the right output
5. The code in leetcode worked (gave the wrong answer but worked) when I initialized the first node of list3 also in the heap
6. used a function to create nodes. 7ms- faster than 87.80% online submissions. memory usage - 15.1Mb - less than 7.87 % online submissions
7. Things to keep in mind: Don’t repeat conditions that have already been checked once - redundancy Pass pointers by reference if you’re playing with the pointer values themselves, and not what is stored at the address they are pointing to

Twosum

first code:

change that needs to be made: instead of making an entirely new array of nums2, we somehow incorporate increasing each number by the value of least inside the hash function.

second code:

has time complexity O(n) but is still slower than most online submissions

third code:

used unordered_map. Code reduced to a single for loop due to fast storage and retrieval of maps and less lines of code. Everything condensed to a single for loop.

SortList

The first code:

used bubble sort; worked for basic cases, but not for an input = [] so added an if statement to directly return if the head is a nullptr

The second code:

Used bubble sort; worked for basic cases; exceeded the time limit for cases with large inputs(beacause bubble sort) So switched to quicksort but quicksort showed an error

The third code:

The quicksort error: heap buffer overflow