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.
Example:
Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:
1 <---
/ \
2 3 <---
\ \
5 4 <---
A:
我所能想到的,就是简单的bfs (dfs)
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<Integer> rightSideView(TreeNode root) {
List<Integer> list = new LinkedList<Integer>();
Queue<TreeNode> queue = new LinkedList();
if(root == null)
return list;
queue.add(root);
while( queue.isEmpty() == false){
Queue<TreeNode> newQueue = new LinkedList();
boolean isFirst = true;
while( ! queue.isEmpty()){
TreeNode node = queue.poll();
if(isFirst){
list.add(node.val);
isFirst = false;
}
if(node.right != null)
newQueue.add(node.right);
if(node.left != null)
newQueue.add(node.left);
}
queue = newQueue;
}
return list;
}
}
***********dfs ****************
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
vector<int> rightSideView(TreeNode* root) {
vector<int> res;
helper(root, 1, res);
return res;
}
private:
void helper(TreeNode * root, int depth, vector<int> & res){
if(!root)
return;
if(res.size() < depth){
res.push_back(root->val);
}
helper(root->right, depth+1, res);
helper(root->left, depth+1, res);
}
};
Mistakes:
Learned: