173.二叉搜索树迭代器

本题就是实现二叉树的中序遍历，利用数组本身实现迭代器

/*** 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 BSTIterator {private int idx;private List<Integer> arr;public BSTIterator(TreeNode root) {idx = 0;arr = new ArrayList<>();inorderTravel(root,arr);}public int next() {return arr.get(idx++);}public boolean hasNext() {return idx < arr.size();}//中序遍历public void inorderTravel(TreeNode root,List<Integer> arr){if(root == null){return;}inorderTravel(root.left,arr);arr.add(root.val);inorderTravel(root.right,arr);}
}/*** Your BSTIterator object will be instantiated and called as such:* BSTIterator obj = new BSTIterator(root);* int param_1 = obj.next();* boolean param_2 = obj.hasNext();*/