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MergeKLinkedLists.cpp
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MergeKLinkedLists.cpp
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/*
* Laurie Kirk 8-105-20
* Merges k linked lists into a single one
* Time complexity: O(n*k^2)
*/
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* mergeKLists(vector<ListNode*>& lists) {
ListNode* merged_lists_head = NULL;
ListNode* merged_lists_tail = NULL; // Since we will be constantly inserting at tail
bool all_lists_empty = false;
int min_index = -1; // Index of next list to grab element from
int i; // Declaring the loop variable so it can be referenced elsewhere
while (!all_lists_empty)
{
min_index = -1;
// Find the next smallest element to add to our list
for (int i = 0; i < lists.size(); ++i)
{
if (lists[i] == NULL)
{
lists.erase(lists.begin() + i);
--i; // Account for the erase
}
else if (min_index == -1)
min_index = i;
else if (lists[i]->val < lists[min_index]->val)
min_index = i;
}
// Check if we have no more elements
if (min_index == -1)
all_lists_empty = true;
else
{
// Otherwise, add the next node and remove it
add_node(&merged_lists_head, &merged_lists_tail, lists[min_index]->val);
lists[min_index] = lists[min_index]->next;
}
}
return merged_lists_head;
}
/*
Adds a single node to the tail of the list
*/
void add_node(ListNode** head, ListNode** tail, int new_value)
{
// Create a new node to add
ListNode *new_node = new ListNode();
new_node->val = new_value;
new_node->next = NULL;
// If this is the first node added
if (*head == NULL)
{
*head = new_node;
*tail = new_node;
} else
{
// Add to the end of the list
(*tail)->next = new_node;
*tail = new_node;
}
}
};