/** * 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 convertBST(TreeNode root) { traverse(root); return root; } int sum = 0; void traverse(TreeNode root){ if(root == null){ return; } traverse(root.right); sum+= root.val; root.val = sum; traverse(root.left); } }