标签:10 right TreeNode val list lt 二叉树 root left
今天刚做了二叉树的前序遍历在这里总结一下二叉树遍历,利用递归解法。
递归思想打掉二叉树遍历操作:
前序遍历
/**
* 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> list = new ArrayList<Integer>();
traversal(root,list);
return list;
}
public void traversal(TreeNode root,List<Integer> list){
if(root == null){
return;
}
//根
list.add(root.val);
//左
traversal(root.left,list);
//右
traversal(root.right,list);
}
}
中序遍历
/**
* 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) {
//二叉树的终须遍历 左根右
List<Integer> result = new ArrayList<>();
traversal(root,result);
return result;
}
public void traversal(TreeNode root,List<Integer> list){
if (root==null){
return;
}
//左
inorder(root.left,list);
//根
list.add(root.val);
//右
inorder(root.right,list);
}
}
后续遍历
/**
* 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> postorderTraversal(TreeNode root) {
List<Integer> list = new ArrayList<Integer>();
traversal(root,list);
return list;
}
public void traversal(TreeNode root,List<Integer> list){
if(root == null){
return;
}
//左
traversal(root.left,list);
//右
traversal(root.right,list);
list.add(root.val);
}
}
层次遍历
层次遍历是对二叉树进行一层一层的遍历
/**
* 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 {
List<List<Integer>> levels = new ArrayList<List<Integer>>();
public List<List<Integer>> levelOrder(TreeNode root) {
if (root == null) return new ArrayList<>();
levelOrderDepth(root, 0);
return levels;
}
//进行层序遍历
public void levelOrderDepth(TreeNode root,int level) {
//如果当前levels的长度 和 level相等
if (levels.size() == level) {
levels.add(new ArrayList<>());
}
levels.get(level).add(root.val);
if (root.left != null) {
levelOrderDepth(root.left,level+1);
}
if (root.right != null) {
levelOrderDepth(root.right,level+1);
}
}
}
递归遍历是比较好想的;然后在进行二叉树的层序遍历或者深度的查找时,往往会借用到队列进行解决。使用队列进行一层一层的迭代处理,先进先出的属性
/**
* 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<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) {
return res;
}
//队列操作
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
//进行遍历树
List<Integer> list = new ArrayList<>();
int len = queue.size();
for (int i = 0;i<len; i++) {
TreeNode node = queue.poll();
list.add(node.val);
if (node.left != null) {
queue.offer(node.left);
}
if (node.right != null) {
queue.offer(node.right);
}
}
res.add(list);
}
return res;
}
}
标签:10,right,TreeNode,val,list,lt,二叉树,root,left 来源: https://blog.csdn.net/qq_35746739/article/details/121136057
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