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test32.java
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package byteDance;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
/**
* Created by lizeyang on 2020/5/15.
* 二叉树的各层节点数
*/
public class test32 {
//非递归实现
public static List<Integer> test(TreeNode root) {
List<Integer> list = new ArrayList<>();
if (root == null) {
return list;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
int size = queue.size();
list.add(size);
for (int i = 0; i < size; i++) {
TreeNode node = queue.poll();
if (node.left != null) {
queue.offer(node.left);
}
if (node.right != null) {
queue.offer(node.right);
}
}
}
return list;
}
//递归实现
static List<List<Integer>> res = new ArrayList<>();
public static List<Integer> levelTraverse(TreeNode root){
List<Integer> list = new ArrayList<>();
if(root==null){
return new ArrayList<>();
}
int depth = getDepth(root);
for(int i=0;i<depth;i++){
res.add(new ArrayList<>());
}
printNodeAtLevel(root,res,0);
for(int i=0;i<res.size();i++) {
list.add(res.get(i).size());
}
return list;
}
public static void printNodeAtLevel(TreeNode root,List<List<Integer>> res,int level){
if(root==null){
return;
}
res.get(level).add(root.val);
printNodeAtLevel(root.left,res,level+1);
printNodeAtLevel(root.right,res,level+1);
}
public static int getDepth(TreeNode root){
if(root==null){
return 0;
}
if(root.left==null){
return getDepth(root.right)+1;
}
if(root.right==null){
return getDepth(root.left)+1;
}
return Math.max(getDepth(root.left),getDepth(root.right))+1;
}
public static void main(String[] args) {
TreeNode root = new TreeNode(5);
root.left = new TreeNode(4);
root.right = new TreeNode(8);
root.left.left = new TreeNode(3);
root.right.left = new TreeNode(7);
root.right.left.left = new TreeNode(6);
root.right.right = new TreeNode(9);
//非递归调用
// List<Integer> res = test(root);
//递归调用
List<Integer> res = levelTraverse(root);
for (int i = 0; i < res.size(); i++) {
System.out.print(res.get(i) + " ");
}
}
}