本题与求二叉树层序遍历类似,只需要在该解法上判断当前遍历的层数,并在相应层次进行反转即可
import java.util.*;
/*
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
*/
public class Solution {
public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
if(pRoot == null){
return new ArrayList<>();
}
Queue<TreeNode> q = new LinkedList<>();
ArrayList<ArrayList<Integer>> result = new ArrayList<>();
q.offer(pRoot);
int level = 0;
while(!q.isEmpty()){
int len = q.size();
ArrayList<Integer> list = new ArrayList<>();
for(int i = 0;i<len;i++){
TreeNode temp = q.poll();
list.add(temp.val);
if(temp.left != null){
q.offer(temp.left);
}
if(temp.right != null){
q.offer(temp.right);
}
}
if(level % 2 == 1){
Collections.reverse(list);
}
level++;
result.add(list);
}
return result;
}
}