【LeeCode】⼆叉树的序遍历

144.⼆叉树的前序遍历

【题目描述】

给你二叉树的根节点 ​​root​​ ，返回它节点值的 前序 遍历。

【示例】

【代码】admin

package com.company;

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

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 {
    List<Integer> list = new ArrayList<>();
    public List<Integer> preorderTraversal(TreeNode root) {
        // 前序: 根左右
        if (root == null) return list;
        preOrder(root);
        return list;

    }

    public void preOrder(TreeNode root){
        if (root == null) return;
        list.add(root.val);
        preOrder(root.left);
        preOrder(root.right;
    }
}

public class Test {
    public static void main(String[] args) {

    }
}

145.二叉树的后序遍历

【代码】admin

class Solution {
List<Integer> list = new ArrayList<>();
public List<Integer> postorderTraversal(TreeNode root) {
if (root == null) return list;
postOrder(root);
return list;
    }
// 后序: 左右根
public void postOrder(TreeNode root){
if (root == null) return;

postOrder(root.left);
postOrder(root.right);
list.add(root.val);
    }
}

94.⼆叉树的中序遍历

【代码】admin

class Solution {
    List<Integer> list = new ArrayList<>();
    public List<Integer> inorderTraversal(TreeNode root) {
        if (root == null) return list;
        postOrder(root);
        return list;
    }
    // 中序: 左根右
    public void postOrder(TreeNode root){
        if (root == null) return;
        postOrder(root.left);
        list.add(root.val);
        postOrder(root.right);

    }
}

学习参考

​​https://leetcode.cn/problems/binary-tree-preorder-traversal/solutions/461821/er-cha-shu-de-qian-xu-bian-li-by-leetcode-solution/​​

​​https://leetcode.cn/problems/binary-tree-preorder-traversal/solutions/87526/leetcodesuan-fa-xiu-lian-dong-hua-yan-shi-xbian-2/​​