Careercup - Google面试题 - 5205167846719488

2014-05-03 23:35

题目链接

原题：

For a given node in binary search tree find a next largest number in search tree.

题目：给定一个二叉搜索树的节点，找出此节点在树中的中序后继节点，也就是比它大的最小节点。

解法：右子树向左走到底，左祖先走到顶向右。草稿纸上一画图就清楚了。

代码：

 // http://www.careercup.com/question?id=5205167846719488
 struct TreeNode {
     int val;
     TreeNode *left;
     TreeNode *right;
     TreeNode(int _val = ): val(_val), left(nullptr), right(nullptr) {};
 };

 class Solution {
 public:
     int nextLargestNumber(TreeNode *root, int val) {
         if (root == nullptr) {
             // nothing to do
             return val;
         }

         left_top = nullptr;
         return findRecursive(root, val);
     }
 private:
     TreeNode *left_top;

     int findRecursive(TreeNode *root, int val) {
         if (root == nullptr) {
             // not found, return val
             return val;
         } else if (root->val > val) {
             left_top = root;
             return findRecursive(root->left, val);
         } else if (root->val < val) {
             return findRecursive(root->right, val);
         } else {
             if (left_top == nullptr) {
                 // val is the greatest of all.
                 return val;
             }
             if (root->right == nullptr) {
                 return left_top->val;
             }

             left_top = root->right;
             while (left_top->left != nullptr) {
                 left_top = left_top->left;
             }
             return left_top->val;
         }
     };
 }