The basic idea is to get the last node of each level in the tree. Using the BFS can help us easily reach this goal.

```
/**
* 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) return res;
queue<TreeNode*> q;
q.push(root);
while(q.size())
{
int n = q.size();
TreeNode* top;
for(int i = 0; i < n; ++i)
{
top = q.front();
q.pop();
if(top->left) q.push(top->left);
if(top->right) q.push(top->right);
}
res.push_back(top->val);
}
return res;
}
};
```