Leetcode#148 Sort List

原题地址

链表归并排序

真是恶心的一道题啊，哇了好多次才过。

代码：

void mergeList(ListNode *a, ListNode *b, ListNode *&h, ListNode *&t) {
  h = t = NULL;
  while (a && b) {
    ListNode *c = NULL;
    if (a->val <= b->val) {
      c = a;
      a = a->next;
    }
    else {
      c = b;
      b = b->next;
    }
    if (!h)
      h = t = c;
    else {
      t->next = c;
      t = t->next;
    }
  }
  while (a) {
    t->next = a;
    t = t->next;
    a = a->next;
  }
  while (b) {
    t->next = b;
    t = t->next;
    b = b->next;
  }
}
    
ListNode *sortList(ListNode *head) {
  ListNode *prev = NULL;
  ListNode *h1 = NULL;
  ListNode *h2 = NULL;
  ListNode *t1 = NULL;
  ListNode *t2 = NULL;
  ListNode *node = NULL;
  int len = 0;
        
  node = head;
  while (node && (++len))
    node = node->next;
            
  for (int l = 1; l < len; l <<= 1) {
    prev = NULL;
    h1 = NULL;
    h2 = NULL;
    t1 = NULL;
    t2 = NULL;
    node = head;
            
    while (node) {
      h1 = t1 = node;
      for (int i = 0; node && i < l; i++) {
        t1 = node;
        node = node->next;
      }
      if (t1)
        t1->next = NULL;
      h2 = t2 = node;
      for (int i = 0; node && i < l; i++) {
        t2 = node;
        node = node->next;
      }
      if (t2)
        t2->next = NULL;
                
      ListNode *h, *t;
      if (h2)
        mergeList(h1, h2, h, t);
      else {
        h = h1;
        t = t1;
      }
      if (!prev)
        head = h;
      else
        prev->next = h;
      t->next = node;
      prev = t;
    }
  }
        
  return head;
}