Leetcode#109 Convert Sorted List to Binary Search Tree

原题地址

 

跟Convert Sorted Array to Binary Search Tree（参见这篇文章）类似，只不过用list就不能随机访问了。

 

代码：

TreeNode *buildBST(ListNode *head, int len) {
  if (len <= 0)
    return NULL;

  ListNode *p = head;
  int leftLen = 1;
  while (leftLen * 2 < len) {
    p = p->next;
    leftLen++;
  }
  TreeNode *node = new TreeNode(p->val);
  node->left = buildBST(head, leftLen - 1);
  node->right = buildBST(p->next, len - leftLen);

  return node;
}

TreeNode *sortedListToBST(ListNode *head) {
  ListNode *node = head;
  int len = 0;

  while (node) {
    node = node->next;
    len++;
  }
  return buildBST(head, len);
}