[LeetCode] 538.Convert BST to Greater Tree

[LeetCode] 538.Convert BST to Greater Tree

• 题目描述
• 解题思路
• 实验代码

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题目描述

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

这道题依然是要用递归的方法。想要解决这道题首先要对二叉搜索树作一个了解。二叉搜索树的特点是：若它的左子树不空，则左子树上所有结点的值均小于它的根结点的值； 若它的右子树不空，则右子树上所有结点的值均大于它的根结点的值。知道这个特点以后这道题就得到了简化和理解。左子节点加上它父节点和右兄弟的值，父节点加上右子节点的值。这道题就得到了解决。

实验代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int sum = 0;
    void travel(TreeNode* root) {
        if (!root) return;
        if (root->right)
            travel(root->right);
        sum += root->val;
        root->val = sum;
        if (root->left)
            travel(root->left);
    }
    TreeNode* convertBST(TreeNode* root) {
        travel(root);
        return root;
    }
};