LeetCode36|二叉树的右视图

输入: [1,2,3,null,5,null,4]
输出: [1, 3, 4]
解释:

   1            <---
 /   
2     3         <---
      
  5     4       <---

 

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class RightSideViewTest {
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(1);
        TreeNode t2 = new TreeNode(2);
        TreeNode t3 = new TreeNode(3);
        TreeNode t4 = new TreeNode(4);
        TreeNode t5 = new TreeNode(5);
        t1.left = t2;
        t1.right = t3;
        t2.right = t5;
        t3.right = t4;
        List<Integer> list = rightSideView(t1);
        System.out.println("list = " + list);

    }

    public static List<Integer> rightSideView(TreeNode root) {
        List<Integer> totalList = new ArrayList<>();
        List<List<Integer>> listList = new ArrayList<>();
        if (root == null) {
            return totalList;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            List<Integer> list = new ArrayList<>();
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                list.add(node.val);
                if (node.left != null) {
                    queue.add(node.left);
                }
                if (node.right != null) {
                    queue.add(node.right);
                }
            }
            listList.add(list);
        }
        for (List<Integer> list : listList) {
            totalList.add(list.get(list.size() - 1));
        }

        return totalList;
    }
}