1038.把二叉搜索树转换为累加树.js

/*
 * @lc app=leetcode.cn id=1038 lang=javascript
 *
 * [1038] 把二叉搜索树转换为累加树
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {TreeNode}
 */
var bstToGst = function(root) {
  let sum = 0;

  const traverse = (root) => {
    if (root === null) return;
    traverse(root.right);
    sum += root.val;
    root.val = sum;
    traverse(root.left);
  }

  traverse(root);
  return root;
};
// @lc code=end