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

解答

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public class Solution {
    int sum = 0;
    public TreeNode convertBST(TreeNode root) {
        convert(root);
        return root;
    }
    public void convert(TreeNode cur) {
        if (cur == null) return;
        convert(cur.right);
        cur.val += sum;
        sum = cur.val;
        convert(cur.left);
    }
}