[leetcode] Binary Tree Right Side View

dfs，记录已经访问到的层数即可。代码如下：

vector<int> rightSideView(TreeNode *root) {
vector<int> result;
int curLevel = 0, level = -1;
dfs(result, curLevel, level, root);
return result;
}
void dfs(vector<int> &result, int curLevel, int &level, TreeNode *root){
if(!root)
return;
if(curLevel > level){
result.push_back(root->val);
++level;
}
dfs(result, curLevel + 1, level, root->right);
dfs(result, curLevel + 1, level, root->left);
}