[LeetCode] 199. Binary Tree Right Side View

 Problem : https://leetcode.com/problems/binary-tree-right-side-view/

Use BFS to traverse the tree

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def rightSideView(self, root: TreeNode) -> List[int]:
        if not root : return []
        
        result = []
        
        queue = deque([root])
        while queue:
            N = len(queue)
            for i in range(N):
                node = queue.popleft()
                if node.left:
                    queue.append(node.left)
                    
                if node.right:
                    queue.append(node.right)
                
                # append the right-most node value
                if i == N-1:
                    result.append(node.val)
                    
        return result

DFS Solution:

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def rightSideView(self, root: TreeNode) -> List[int]:
        
        if not root: return []
        
        result = []
        
        # dfs
        stack = [(root, 0)]
        
        while stack:
            node, level = stack.pop()
            
            if level == len(result):
                result.append(node.val)
            
            if node.left:
                stack.append((node.left, level+1))
                
            if node.right:
                stack.append((node.right, level+1))
                    
        return result

Edited on 05/31/2021. Add DFS solution.