问题描述
Given a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus sum of all keys greater than the original key in BST.
Example:
Input: The root of a Binary Search Tree like this: 5 / \ 2 13 Output: The root of a Greater Tree like this: 18 / \ 20 13
解题思路
后序遍历BST然后把节点值逐个累加即可。
代码如下
class Solution { public: TreeNode* convertBST(TreeNode* root) { if (root == NULL) return NULL; int sum = 0; backorder(root, sum); return root; } private: void backorder(TreeNode *r, int &sum) { if (r != NULL) { backorder(r->right, sum); r->val += sum; sum = r->val; backorder(r->left, sum); } } };