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leetcode 94 Solution

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代码解析

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package com.demo.s94;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

/**
 * 二叉树的中序遍历
 * 给定一个二叉树的根节点 root ，返回 它的 中序 遍历 。
 */
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;
    }
}
public class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        if (root == null){
            return result;
        }
        //栈 存节点
        Stack<TreeNode> stack = new Stack<>();
        //由根节点开始遍历
        TreeNode cur = root;
        // 当前节点为null
        while (cur != null || !stack.isEmpty()){
            if (cur != null){
                //遍历左节点 节点压栈
                stack.push(cur);
                cur = cur.left;
            }else{
                //遍历完左分支，把左分支弹出遍历右分支
                cur = stack.pop();
                result.add(cur.val);
                //遍历右分支
                cur = cur.right;
            }
        }
        return result;
    }
}