From 440e04fffe7bc5cfacd11653fc6f0d3704382767 Mon Sep 17 00:00:00 2001 From: Kelvin Date: Thu, 29 Jul 2021 15:50:46 -0400 Subject: [PATCH] =?UTF-8?q?=E6=9B=B4=E6=94=B9=200112.=E8=B7=AF=E5=BE=84?= =?UTF-8?q?=E6=80=BB=E5=92=8C.md=20Python3=20=E4=BB=A3=E7=A0=81.?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 0112.路径总和: 1. 修改了 python3 注释, 更改代码格式. 2. 增加了迭代方法Python3代码. 0113.路径总和-ii: 上一版python3代码的问题: (1)注释一般不用// (2)代码格式有些不规范. (3)内层函数命名也不是特别的informative. 新版本代码修改了上述问题. 本次提交代码均已通过leetcode测试. --- problems/0112.路径总和.md | 113 ++++++++++++++++++++++------------ 1 file changed, 72 insertions(+), 41 deletions(-) diff --git a/problems/0112.路径总和.md b/problems/0112.路径总和.md index ae9a9267..474e17da 100644 --- a/problems/0112.路径总和.md +++ b/problems/0112.路径总和.md @@ -416,6 +416,8 @@ class Solution { Python： 0112.路径总和 + +**递归** ```python # Definition for a binary tree node. # class TreeNode: @@ -424,28 +426,56 @@ Python： # self.left = left # self.right = right -// 递归法 - class Solution: def hasPathSum(self, root: TreeNode, targetSum: int) -> bool: - def isornot(root,targetSum)->bool: - if (not root.left) and (not root.right) and targetSum == 0:return True // 遇到叶子节点，并且计数为0 - if (not root.left) and (not root.right):return False //遇到叶子节点，计数不为0 + def isornot(root, targetSum) -> bool: + if (not root.left) and (not root.right) and targetSum == 0: + return True # 遇到叶子节点，并且计数为0 + if (not root.left) and (not root.right): + return False # 遇到叶子节点，计数不为0 if root.left: - targetSum -= root.left.val //左节点 - if isornot(root.left,targetSum):return True //递归，处理左节点 - targetSum += root.left.val //回溯 + targetSum -= root.left.val # 左节点 + if isornot(root.left, targetSum): return True # 递归，处理左节点 + targetSum += root.left.val # 回溯 if root.right: - targetSum -= root.right.val //右节点 - if isornot(root.right,targetSum):return True //递归，处理右节点 - targetSum += root.right.val //回溯 + targetSum -= root.right.val # 右节点 + if isornot(root.right, targetSum): return True # 递归，处理右节点 + targetSum += root.right.val # 回溯 return False - - if root == None:return False //别忘记处理空TreeNode - else:return isornot(root,targetSum-root.val) + + if root == None: + return False # 别忘记处理空TreeNode + else: + return isornot(root, targetSum - root.val) ``` +**迭代 - 层序遍历** +```python +class Solution: + def hasPathSum(self, root: TreeNode, targetSum: int) -> bool: + if not root: + return False + + stack = [] # [(当前节点，路径数值), ...] + stack.append((root, root.val)) + + while stack: + cur_node, path_sum = stack.pop() + + if not cur_node.left and not cur_node.right and path_sum == targetSum: + return True + + if cur_node.right: + stack.append((cur_node.right, path_sum + cur_node.right.val)) + + if cur_node.left: + stack.append((cur_node.left, path_sum + cur_node.left.val)) + + return False +``` 0113.路径总和-ii + +**递归** ```python # Definition for a binary tree node. # class TreeNode: @@ -453,35 +483,36 @@ class Solution: # self.val = val # self.left = left # self.right = right -//递归法 class Solution: def pathSum(self, root: TreeNode, targetSum: int) -> List[List[int]]: - path=[] - res=[] - def pathes(root,targetSum): - if (not root.left) and (not root.right) and targetSum == 0: // 遇到叶子节点，并且计数为0 - res.append(path[:]) //找到一种路径，记录到res中，注意必须是path[:]而不是path - return - if (not root.left) and (not root.right):return // 遇到叶子节点直接返回 - if root.left: //左 - targetSum -= root.left.val - path.append(root.left.val) //递归前记录节点 - pathes(root.left,targetSum) //递归 - targetSum += root.left.val //回溯 - path.pop() //回溯 - if root.right: //右 - targetSum -= root.right.val - path.append(root.right.val) //递归前记录节点 - pathes(root.right,targetSum) //递归 - targetSum += root.right.val //回溯 - path.pop() //回溯 - return - - if root == None:return [] //处理空TreeNode - else: - path.append(root.val) //首先处理根节点 - pathes(root,targetSum-root.val) - return res + + def traversal(cur_node, remain): + if not cur_node.left and not cur_node.right and remain == 0: + result.append(path[:]) + return + + if not cur_node.left and not cur_node.right: return + + if cur_node.left: + path.append(cur_node.left.val) + remain -= cur_node.left.val + traversal(cur_node.left, remain) + path.pop() + remain += cur_node.left.val + + if cur_node.right: + path.append(cur_node.right.val) + remain -= cur_node.right.val + traversal(cur_node.right, remain) + path.pop() + remain += cur_node.right.val + + result, path = [], [] + if not root: + return [] + path.append(root.val) + traversal(root, targetSum - root.val) + return result ``` Go：