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988. Smallest String Starting From Leaf/988. Smallest String Starting From Leaf.py
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""" | ||
You are given the root of a binary tree where each node has a value in the range [0, 25] representing the letters 'a' to 'z'. | ||
Return the lexicographically smallest string that starts at a leaf of this tree and ends at the root. | ||
As a reminder, any shorter prefix of a string is lexicographically smaller. | ||
For example, "ab" is lexicographically smaller than "aba". | ||
A leaf of a node is a node that has no children. | ||
Example 1: | ||
Input: root = [0,1,2,3,4,3,4] | ||
Output: "dba" | ||
Example 2: | ||
Input: root = [25,1,3,1,3,0,2] | ||
Output: "adz" | ||
Example 3: | ||
Input: root = [2,2,1,null,1,0,null,0] | ||
Output: "abc" | ||
Constraints: | ||
The number of nodes in the tree is in the range [1, 8500]. | ||
0 <= Node.val <= 25 | ||
""" | ||
# 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 smallestFromLeaf(self, root: Optional[TreeNode]) -> str: | ||
q,result = collections.deque(),None | ||
q.append((root,chr(root.val+97))) | ||
while q: | ||
node,path = q.popleft() | ||
if not node.left and not node.right: | ||
if not result: | ||
result = path | ||
else: | ||
result = min(result,path) | ||
if node.left: q.append((node.left,chr(node.left.val+97)+path)) | ||
if node.right: q.append((node.right,chr(node.right.val+97)+path)) | ||
return result |