LeetCode 热题100-37-二叉树的中序遍历

核心思想：中序遍历
递归版本：

/**
 * 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 List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<>();
        inOrder(root,list);
        return list;
    }
    void inOrder(TreeNode root, List<Integer> list) {
        if (root != null) {
            inOrder(root.left, list);
            list.add(root.val);
            inOrder(root.right, list);
        }
    }
}

迭代版：

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<>();
        Deque<TreeNode> deque = new ArrayDeque<>();
        while(root!=null || !deque.isEmpty()){
            while(root != null){
                deque.addLast(root);
                root = root.left;
            }
            root = deque.peekLast();
            list.add(deque.pollLast().val);
            root = root.right;
        }
        return list;
    }
}

morris版本（想去字节就看）：

明天就写