LeetCode - Binary Tree Right Side View

解法一： recursion

class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        if(!root) return {};
        vector<int> left = rightSideView(root->left);
        vector<int> right = rightSideView(root->right);
        int l = left.size();
        int r = right.size();
        if(l>r){
            right.insert(right.end(), left.begin()+right.size(), left.end());
        }
        right.insert(right.begin(), root->val);
        return right;
    }
};

解法二：non-recursion

class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> res;
        if(!root) return res;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            res.push_back(q.back()->val);
            int s = q.size();
            for(int i=0;i<s;i++){
                TreeNode* t = q.front(); q.pop();
                if(t->left) q.push(t->left);
                if(t->right) q.push(t->right);
            }
        }
        return res;

    }
};