4道经典二叉树相关题目-侧面观察二叉树

class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<TreeNode* > a;
        vector<int> re;
        if(!root) return re;
        a.push_back(root);
        if(!root->left && !root->right) {re.push_back(root->val); return re;}

        int l = 0 , r = 1;
        while(l < r){
            for(int i = l ; i < r; i++){
                if(a[i]->left) a.push_back(a[i]->left);
                if(a[i]->right) a.push_back(a[i]->right);
            }
            re.push_back(a[r-1]->val);
            l = r;
            r = a.size();
        }
        return re;
    }
};