動機
複習dfs
Problem
Given a binary tree, find its minimum depth.
The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
Note: A leaf is a node with no children.
Example 1:
Input: root = [3,9,20,null,null,15,7]Output: 2
Example 2:
Input: root = [2,null,3,null,4,null,5,null,6]Output: 5
Constraints:
- The number of nodes in the tree is in the range
[0, 105]
. -1000 <= Node.val <= 1000
Sol
def dfs(r):
if r is None:
return float('inf')
elif r.left is None and r.right is None:
return 1
else:
return min(dfs(r.left),dfs(r.right))+1
class Solution:
def minDepth(self, r: TreeNode) -> int:
if not r:
return 0
else:
return dfs(r)