23.md

23 Merge k Sorted Lists

It's a little easy way, to choose a the min answer in all list, and let the chosen list start point ++; And repeat until all list has be appended to the answer list.

I think the code is all right. However it show me stack buffer overflow. I need to debug it tomorrow.

However, it's not an efficient way to find the min.

We can maintain a heap to get the min. Each time we find the min, and add the head of the list to the heap each time.

I copy other's standard code in the 23_heap.cpp. (\ref https://blog.csdn.net/Ethan95/article/details/85195403)

I found my problem!!! I decide whether the answer is NULL

original code

if (answer == NULL){
                answer = tmp;
                head = answer;
            }else{
                answer->next = tmp;
                answer = answer->next;
            }

Code now

answer->next = tmp;
            answer = answer ->next;
            current[index] = current[index] -> next;

In the before code, I use a NULL to decide a pointer. I think maybe leetcode do not approve that behavior.