LeetCode 199. Binary Tree Right Side View

题目链接

199. Binary Tree Right Side View

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].

解：层次遍历，为每个节点加一个层号，每次弹出队列时，判断是否和队头的层号不同（是否是最右的），如果是将值加入结果中，代码：

/**
 * 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) {
        queue<pair<int, TreeNode*> > q;
        pair<int, TreeNode*> temp;
        vector<int> result;
        if (!root) return result;
        q.push(make_pair(0, root));
        while (!q.empty()) {
            temp = q.front();
            q.pop();
            if (temp.second->left != NULL) q.push(make_pair(temp.first+1, temp.second->left));
            if (temp.second->right != NULL) q.push(make_pair(temp.first+1, temp.second->right));
            if (q.empty() || q.front().first != temp.first) result.push_back(temp.second->val);
        }
        return result;
    }
};