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# 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:
Thought Process:
Way1: BFS
Put the last node in the same level order in to list
/ \
2 3
using bfs and put node in the same level into a list we can have
ans = [[1],[2,3]]
And we always get the last node in the same level
ans = [i[-1] for i in ans]
Way2: DFS
start from root node -> right subtree -> left subtree
With this order, the fisr node we traversed in each detph(1, 2, 3...) is what we want
def rightSideView(self, root: TreeNode) -> List[int]:
T:O(n) since each node is only visited once but it has two passes
S:O(h) if it's balanced tree
if not root:
return []
q = collections.deque([(root, 1)])
ordered_from_top_to_bottom = []
while len(q) != 0:
cur_node, depth = q.popleft()
if cur_node.left:
q.append((cur_node.left, depth+1))
if cur_node.right:
q.append((cur_node.right, depth+1))
while len(ordered_from_top_to_bottom) < depth:
return [ls_node_in_same_level[-1] for ls_node_in_same_level in ordered_from_top_to_bottom]
def rightSideView(self, root: TreeNode) -> List[int]:
if not root:
return []
self.ordered_from_top_to_bottom = []
def dfs(r, depth = 1):
if r:
if depth > len(self.ordered_from_top_to_bottom):
dfs(r.right, depth+1)
dfs(r.left, depth+1)
dfs(root, 1)
return self.ordered_from_top_to_bottom
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