二叉树的前序遍历，中序遍历，后序遍历代码

来源：互联网发布：定时短信软件编辑：程序博客网时间：2024/04/28 14:43

前序遍历

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List<Integer> preorderTraversal(TreeNode root) {        List<Integer> ans=new LinkedList<Integer>();        Stack<TreeNode> stack= new Stack<TreeNode>();        if(root!=null) stack.push(root);        while(!stack.isEmpty())        {            TreeNode node=stack.pop();            ans.add(node.val);            if(node.right!=null) stack.push(node.right);            if(node.left!=null) stack.push(node.left);        }        return ans;    }}

中序遍历

public class Solution {    public List<Integer> inorderTraversal(TreeNode root) {        List<Integer> ans=new LinkedList<Integer>();        Stack<TreeNode> stack=new Stack<TreeNode>();        while(true){            while(root!=null)            {                stack.push(root);                root=root.left;            }            if(stack.isEmpty()) break;            TreeNode node=stack.pop();            ans.add(node.val);            root=node.right;        }        return ans;    }}

后序遍历

public class Solution {    public List<Integer> postorderTraversal(TreeNode root) {    Stack<TreeNode> stack = new Stack<>();    stack.push(root);    List<Integer> ans = new ArrayList<>();    while (!stack.isEmpty()) {        TreeNode node = stack.pop();        if (node != null) {            ans.add(node.val);            stack.push(node.left);            stack.push(node.right);        }    }    Collections.reverse(ans);    return ans;} }

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