day55（1.6）——leetcode面试经典150

199. 二叉树的右视图

199. 二叉树的右视图

题目：

题解：

/**
 * 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> rightSideView(TreeNode root) {
        //用bfs
        List<Integer> list = new LinkedList<>();
        if(root == null) {
            return list;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(queue.size()>0) {
            int size = queue.size();
            for(int i=0;i<size;i++) {
                TreeNode node = queue.poll();
                if(i==size-1) {
                    list.add(node.val);
                }
                if(node.left != null) {
                    queue.add(node.left);
                }
                if(node.right != null) {
                    queue.add(node.right);
                }
            }
        }
        return list;
    }
}