1038.binary-search-tree-to-greater-sum-tree.cpp

/*
 * @lc app=leetcode id=1038 lang=cpp
 *
 * [1038] Binary Search Tree to Greater Sum Tree
 *
 * https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/description/
 *
 * algorithms
 * Medium (78.45%)
 * Total Accepted:    16.8K
 * Total Submissions: 21.4K
 * Testcase Example:  '[4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]'
 *
 * Given the root of a binary search tree with distinct values, modify it so
 * that every node has a new value equal to the sum of the values of the
 * original tree that are greater than or equal to node.val.
 * 
 * As a reminder, a binary search tree is a tree that satisfies these
 * constraints:
 * 
 * 
 * The left subtree of a node contains only nodes with keys less than the
 * node's key.
 * The right subtree of a node contains only nodes with keys greater than the
 * node's key.
 * Both the left and right subtrees must also be binary search trees.
 * 
 * 
 * 
 * 
 * Example 1:
 * 
 * 
 * 
 * 
 * Input: [4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]
 * Output: [30,36,21,36,35,26,15,null,null,null,33,null,null,null,8]
 * 
 * 
 * 
 * 
 * 
 * 
 * Note:
 * 
 * 
 * The number of nodes in the tree is between 1 and 100.
 * Each node will have value between 0 and 100.
 * The given tree is a binary search tree.
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 */
/**
 * 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;
    void callme(TreeNode* root){
        if(root==NULL)  return;
        callme(root->right);
        root->val = sum += root->val;
        callme(root->left);
    }
    TreeNode* bstToGst(TreeNode* root) {
        sum = 0;
        callme(root);
        return root;
    }
};