diff --git a/problems/0513.找树左下角的值.md b/problems/0513.找树左下角的值.md index 5ff25484..26768c74 100644 --- a/problems/0513.找树左下角的值.md +++ b/problems/0513.找树左下角的值.md @@ -271,52 +271,80 @@ class Solution { ### Python - -递归: +(版本一)递归法 + 回溯 ```python class Solution: def findBottomLeftValue(self, root: TreeNode) -> int: - max_depth = -float("INF") - leftmost_val = 0 + self.max_depth = float('-inf') + self.result = None + self.traversal(root, 0) + return self.result + + def traversal(self, node, depth): + if not node.left and not node.right: + if depth > self.max_depth: + self.max_depth = depth + self.result = node.val + return + + if node.left: + depth += 1 + self.traversal(node.left, depth) + depth -= 1 + if node.right: + depth += 1 + self.traversal(node.right, depth) + depth -= 1 - def __traverse(root, cur_depth): - nonlocal max_depth, leftmost_val - if not root.left and not root.right: - if cur_depth > max_depth: - max_depth = cur_depth - leftmost_val = root.val - if root.left: - cur_depth += 1 - __traverse(root.left, cur_depth) - cur_depth -= 1 - if root.right: - cur_depth += 1 - __traverse(root.right, cur_depth) - cur_depth -= 1 - - __traverse(root, 0) - return leftmost_val ``` -迭代 - 层序遍历: +(版本二)递归法+精简 ```python class Solution: def findBottomLeftValue(self, root: TreeNode) -> int: - queue = deque() - if root: - queue.append(root) - result = 0 - while queue: - q_len = len(queue) - for i in range(q_len): - if i == 0: - result = queue[i].val - cur = queue.popleft() - if cur.left: - queue.append(cur.left) - if cur.right: - queue.append(cur.right) - return result + self.max_depth = float('-inf') + self.result = None + self.traversal(root, 0) + return self.result + + def traversal(self, node, depth): + if not node.left and not node.right: + if depth > self.max_depth: + self.max_depth = depth + self.result = node.val + return + + if node.left: + self.traversal(node.left, depth+1) + if node.right: + self.traversal(node.right, depth+1) +``` + +(版本三) 迭代法 +```python +# 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 +from collections import deque +class Solution: + def findBottomLeftValue(self, root: Optional[TreeNode]) -> int: + queue = deque([root]) + while queue: + size = len(queue) + leftmost = queue[0].val + for i in range(size): + node = queue.popleft() + if node.left: + queue.append(node.left) + if node.right: + queue.append(node.right) + if not queue: + return leftmost + + ``` ### Go