[Modification of in-order traversal algorithm] 1038. From binary search tree to larger sum tree

1038. From binary search tree to larger sum tree

Problem-solving ideas

• Transforming the in-order traversal algorithm
• First traverse the right subtree and then accumulate the value of the current node and then traverse the left subtree.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    
    
    public TreeNode bstToGst(TreeNode root) {
    
    
        // 改造中序遍历算法
        traverse(root);

        return root;
    }


    int sum = 0;

    public void traverse(TreeNode root){
    
    
        if(root == null){
    
    
            return;
        }

        traverse(root.right);
        sum += root.val;


        root.val = sum;// 比他大的所有数字之和
        traverse(root.left);
    }
}