From 0b2312ffec67c90a53feb938a6df5444c41fbc1a Mon Sep 17 00:00:00 2001 From: Kelvin Date: Thu, 29 Jul 2021 09:02:15 -0400 Subject: [PATCH 1/3] =?UTF-8?q?Update=200404.=E5=B7=A6=E5=8F=B6=E5=AD=90?= =?UTF-8?q?=E4=B9=8B=E5=92=8C.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 添加python3 迭代方法的代码. Q: 我为什么要更改当前已有的递归代码? A: 因为我发现当前版本的递归代码跟Carl哥的逻辑不是特别一样. 我承认解题思路千变万化, 但是个人感觉最好最好还是尽量跟Carl的思路一样, 这样方便初学者阅读不同语言编写出来的代码. --- problems/0404.左叶子之和.md | 56 +++++++++++++++++++++++--------- 1 file changed, 41 insertions(+), 15 deletions(-) diff --git a/problems/0404.左叶子之和.md b/problems/0404.左叶子之和.md index aa758367..2a76a461 100644 --- a/problems/0404.左叶子之和.md +++ b/problems/0404.左叶子之和.md @@ -205,25 +205,51 @@ class Solution { Python： -```Python + **递归** -# 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 +```python class Solution: def sumOfLeftLeaves(self, root: TreeNode) -> int: - self.res=0 - def areleftleaves(root): - if not root:return - if root.left and (not root.left.left) and (not root.left.right):self.res+=root.left.val - areleftleaves(root.left) - areleftleaves(root.right) - areleftleaves(root) - return self.res + if not root: + return 0 + + left_left_leaves_sum = self.sumOfLeftLeaves(root.left) # 左 + right_left_leaves_sum = self.sumOfLeftLeaves(root.right) # 右 + + cur_left_leaf_val = 0 + if root.left and not root.left.left and not root.left.right: + cur_left_leaf_val = root.left.val # 中 + + return cur_left_leaf_val + left_left_leaves_sum + right_left_leaves_sum ``` + +**迭代** +```python +class Solution: + def sumOfLeftLeaves(self, root: TreeNode) -> int: + """ + Idea: Each time check current node's left node. + If current node don't have one, skip it. + """ + stack = [] + if root: + stack.append(root) + res = 0 + + while stack: + # 每次都把当前节点的左节点加进去. + cur_node = stack.pop() + if cur_node.left and not cur_node.left.left and not cur_node.left.right: + res += cur_node.left.val + + if cur_node.left: + stack.append(cur_node.left) + if cur_node.right: + stack.append(cur_node.right) + + return res +``` + Go： > 递归法 From 2f412e5c7d3b41b66946d92e699330cb7e5e5036 Mon Sep 17 00:00:00 2001 From: Kelvin Date: Thu, 29 Jul 2021 11:18:26 -0400 Subject: [PATCH 2/3] =?UTF-8?q?=E6=9B=B4=E6=96=B0=20513.=E6=89=BE=E6=A0=91?= =?UTF-8?q?=E5=B7=A6=E4=B8=8B=E8=A7=92=E7=9A=84=E5=80=BC=20python=20?= =?UTF-8?q?=E9=83=A8=E5=88=86=E4=BB=A3=E7=A0=81?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 1. 更改python 递归代码: 上一版本python代码跟卡哥思路不一样, 感觉把不同的解题方法放在这里不方便初学者学习. 所以建议更改. 2. 添加迭代方法代码. --- problems/0513.找树左下角的值.md | 61 +++++++++++++++++++++----- 1 file changed, 49 insertions(+), 12 deletions(-) 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 17d15fde..391118ab 100644 --- a/problems/0513.找树左下角的值.md +++ b/problems/0513.找树左下角的值.md @@ -274,8 +274,9 @@ class Solution { Python： + +**递归法 - 回溯** ```python -//递归法 # Definition for a binary tree node. # class TreeNode: # def __init__(self, val=0, left=None, right=None): @@ -284,17 +285,53 @@ Python： # self.right = right class Solution: def findBottomLeftValue(self, root: TreeNode) -> int: - depth=0 - self.res=[] - def level(root,depth): - if not root:return - if depth==len(self.res): - self.res.append([]) - self.res[depth].append(root.val) - level(root.left,depth+1) - level(root.right,depth+1) - level(root,depth) - return self.res[-1][0] + max_depth = -float("INF") + max_left_value = -float("INF") + + def __traversal(root, left_len): + nonlocal max_depth, max_left_value + + if not root.left and not root.right: + if left_len > max_depth: + max_depth = left_len + max_left_value = root.val + return + + if root.left: + left_len += 1 + __traversal(root.left, left_len) + left_len -= 1 + + if root.right: + left_len += 1 + __traversal(root.right, left_len) + left_len -= 1 + return + + __traversal(root, 0) + + return max_left_value +``` + +**迭代法 - 层序遍历** +```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 ``` Go： From 8c53c48ea87fc2f02934799da6f659a7647eb268 Mon Sep 17 00:00:00 2001 From: Kelvin Date: Thu, 29 Jul 2021 11:21:14 -0400 Subject: [PATCH 3/3] =?UTF-8?q?Revert=20"=E6=9B=B4=E6=96=B0=20513.?= =?UTF-8?q?=E6=89=BE=E6=A0=91=E5=B7=A6=E4=B8=8B=E8=A7=92=E7=9A=84=E5=80=BC?= =?UTF-8?q?=20python=20=E9=83=A8=E5=88=86=E4=BB=A3=E7=A0=81"?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This reverts commit 2f412e5c7d3b41b66946d92e699330cb7e5e5036. --- problems/0513.找树左下角的值.md | 61 +++++--------------------- 1 file changed, 12 insertions(+), 49 deletions(-) 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 391118ab..17d15fde 100644 --- a/problems/0513.找树左下角的值.md +++ b/problems/0513.找树左下角的值.md @@ -274,9 +274,8 @@ class Solution { Python： - -**递归法 - 回溯** ```python +//递归法 # Definition for a binary tree node. # class TreeNode: # def __init__(self, val=0, left=None, right=None): @@ -285,53 +284,17 @@ Python： # self.right = right class Solution: def findBottomLeftValue(self, root: TreeNode) -> int: - max_depth = -float("INF") - max_left_value = -float("INF") - - def __traversal(root, left_len): - nonlocal max_depth, max_left_value - - if not root.left and not root.right: - if left_len > max_depth: - max_depth = left_len - max_left_value = root.val - return - - if root.left: - left_len += 1 - __traversal(root.left, left_len) - left_len -= 1 - - if root.right: - left_len += 1 - __traversal(root.right, left_len) - left_len -= 1 - return - - __traversal(root, 0) - - return max_left_value -``` - -**迭代法 - 层序遍历** -```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 + depth=0 + self.res=[] + def level(root,depth): + if not root:return + if depth==len(self.res): + self.res.append([]) + self.res[depth].append(root.val) + level(root.left,depth+1) + level(root.right,depth+1) + level(root,depth) + return self.res[-1][0] ``` Go：