二叉树的前序遍历
使用递归的方式
/**
* 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> preorderTraversal(TreeNode root) {
List<Integer> res = new ArrayList<Integer>();
preorder(root,res);
return res;
\
}
public void preorder(TreeNode root, List<Integer> res){
if(root==null)return;
res.add(root.val);
preorder(root.left,res);
preorder(root.right,res);
}
}
中序
class Solution {
public List<Integer> inorderTraversal(TreeNode root) {
List<Integer> res = new ArrayList<Integer>();
inorder(root,res);
return res;
}
public void inorder(TreeNode root,List<Integer> res){
if(root==null)return ;
inorder(root.left,res);
res.add(root.val);
inorder(root.right,res);
}
}
后序
class Solution {
public List<Integer> postorderTraversal(TreeNode root) {
List<Integer> res = new ArrayList<Integer>();
postorder(root,res);
return res;
}
public void postorder(TreeNode root,List<Integer> res){
if(root==null)return ;
postorder(root.left,res);
postorder(root.right,res);
res.add(root.val);
}
}
