kth-smallest-element-in-a-bst.js

/**Given the root of a binary search tree, and an integer k, return the kth smallest value (1-indexed) of all the values of the nodes in the tree. */
/**
 * 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
 * @param {number} k
 * @return {number}
 */
 var kthSmallest = function(root, k) {
    let res = 0;
    function dfs(node) {
      if (node.left) {
        dfs(node.left);
      }
      k -= 1;
      if (k === 0) {
        res = node.val;
        return;
      }
      if (node.right) {
        dfs(node.right);
      }
  
    }
        
    dfs(root);    
    return res;
  };