leetcode 199 Binary Tree Right Side View

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本文介绍了一种算法，该算法可以遍历一棵二叉树并返回从顶部到底部的右侧可见节点值。通过使用队列实现层级遍历来解决这个问题。

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

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

You should return [1, 3, 4].

Credits:
Special thanks to @amrsaqr for adding this problem and creating all test cases.

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> res;
		if(root == NULL) return res;

		queue<TreeNode*> q;
		q.push(root);

		int width = 1;

		while(!q.empty()) {
			TreeNode *temp = q.front();
			q.pop();

			if(temp->left!=NULL) {
				q.push(temp->left);
			}
			if(temp->right!=NULL) {
				q.push(temp->right);
			}

			if(--width == 0) {
				width = q.size();
				res.push_back(temp->val);
			}
		}

		return res;
    }
};