23. Merge k Sorted Lists

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

Example:

Input:
[   1->4->5,   1->3->4,   2->6
]
Output: 1->1->2->3->4->4->5->6

/**
 * Definition for singly-linked list.
 */
struct ListNode {
  int val;
  struct ListNode *next;
};

struct ListNode* mergeKLists(struct ListNode** lists, int listsSize) {
  struct ListNode * head = NULL;
  struct ListNode * p = NULL;
  struct ListNode * q = NULL;
  int i=0;
  int j=0;
  while(1) {
    for(i=0; i<listsSize; i++) {
      if(p == NULL || (lists[i] != NULL && p->val > lists[i]->val)) {
        p = lists[i];
        j = i;
      }
    }
    if(p == NULL) break;
    if(head == NULL) {
      head = p;
      q = p;
      p = NULL;
      lists[j] = lists[j]->next;
      continue;
    }
    q->next = p;
    q = q->next;
    p = NULL;
    lists[j] = lists[j]->next;
  }
  return head;
}

坑爹，在判断head == NULL的代码块中忘了移向下一个节点，导致lists[j]->next就是lists[j]。