【leetcode】230. Kth Smallest Element in a BST

Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.

Note:
You may assume k is always valid, 1 ≤ k ≤ BST’s total elements.

var kthSmallest = function(root, k) {   var val;   var flag = true;   var cc = 0;   var dd = 0;   function travel(node){       if(flag===false){           return;       }         if(node.left!==null){           travel(node.left);       }       if(k>1){           k--;       }else if(k===1){           val = node.val;           flag=!flag;           k--;       }       if(node.right!==null){           travel(node.right);       }   }   travel(root);   return val;};