LeetCode_199. Binary Tree Right Side View

LeetCode_199. Binary Tree Right Side View
原题：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]

这题大意就是输出每一层最右端的数据。这题应该有两种方法，一种是递归，一种是非递归。

因为递归想不到判断数据进入Vector的条件，所以只能先用用非递归，层次遍历，设立两个队列分别记录当前层访问结点和下层访问结点，当前层的结点访问完了之后，用下一层的替换到当前层，每次输出当前层最后一个数据。代码如下

vector<int> rightSideView(TreeNode* root) {
        vector<int> result;
        TreeNode* t = root;
        queue<TreeNode*> current;
        queue<TreeNode*> next;
        if(root == NULL)return result;
        result.push_back(root->val);

        if(root->left)current.push(root->left);
        if(root->right)current.push(root->right);
        while(!current.empty()){

            while(!current.empty()){
                if(current.size() == 1)result.push_back(current.front()->val);
                t = current.front();
                current.pop();
                if(t->left)next.push(t->left);
                if(t->right)next.push(t->right);

            }
            while(!next.empty()){
                current.push(next.front());
                next.pop();
            }

        }
        return result;
    }