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Merge pull request #1164 from SianXiaoCHN/master
python3_0941.有效的山脉数组更新双指针方法_0225.用队列实现栈添加单队列优化方法_0112.路径总和精简递归回溯和递归返回条件,添加迭代法_0860.柠檬水找零 去除无用变量
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@ -496,25 +496,20 @@ class solution:
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def pathsum(self, root: treenode, targetsum: int) -> list[list[int]]:
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def traversal(cur_node, remain):
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if not cur_node.left and not cur_node.right and remain == 0:
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result.append(path[:])
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return
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if not cur_node.left and not cur_node.right: return
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if not cur_node.left and not cur_node.right:
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if remain == 0:
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result.append(path[:])
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return
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if cur_node.left:
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path.append(cur_node.left.val)
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remain -= cur_node.left.val
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traversal(cur_node.left, remain)
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traversal(cur_node.left, remain-cur_node.left.val)
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path.pop()
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remain += cur_node.left.val
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if cur_node.right:
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path.append(cur_node.right.val)
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remain -= cur_node.right.val
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traversal(cur_node.right, remain)
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traversal(cur_node.right, remain-cur_node.left.val)
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path.pop()
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remain += cur_node.right.val
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result, path = [], []
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if not root:
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@ -524,6 +519,30 @@ class solution:
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return result
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```
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**迭代法,用第二个队列保存目前的总和与路径**
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```python
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class Solution:
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def pathSum(self, root: Optional[TreeNode], targetSum: int) -> List[List[int]]:
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if not root:
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return []
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que, temp = deque([root]), deque([(root.val, [root.val])])
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result = []
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while que:
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for _ in range(len(que)):
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node = que.popleft()
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value, path = temp.popleft()
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if (not node.left) and (not node.right):
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if value == targetSum:
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result.append(path)
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if node.left:
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que.append(node.left)
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temp.append((node.left.val+value, path+[node.left.val]))
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if node.right:
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que.append(node.right)
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temp.append((node.right.val+value, path+[node.right.val]))
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return result
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```
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## go
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112. 路径总和
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@ -354,6 +354,32 @@ class MyStack:
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return len(self.queue_in) == 0
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```
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优化,使用一个队列实现
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```python
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class MyStack:
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def __init__(self):
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self.que = deque()
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def push(self, x: int) -> None:
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self.que.append(x)
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def pop(self) -> int:
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if self.empty():
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return None
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for i in range(len(self.que)-1):
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self.que.append(self.que.popleft())
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return self.que.popleft()
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def top(self) -> int:
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if self.empty():
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return None
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return self.que[-1]
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def empty(self) -> bool:
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return not self.que
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```
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Go:
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@ -32,7 +32,7 @@
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## 思路
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为了了满足更多的小孩,就不要造成饼干尺寸的浪费。
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为了满足更多的小孩,就不要造成饼干尺寸的浪费。
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大尺寸的饼干既可以满足胃口大的孩子也可以满足胃口小的孩子,那么就应该优先满足胃口大的。
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@ -157,7 +157,7 @@ class Solution {
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```python
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class Solution:
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def lemonadeChange(self, bills: List[int]) -> bool:
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five, ten, twenty = 0, 0, 0
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five, ten = 0, 0
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for bill in bills:
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if bill == 5:
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five += 1
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@ -169,10 +169,8 @@ class Solution:
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if ten > 0 and five > 0:
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ten -= 1
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five -= 1
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twenty += 1
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elif five > 2:
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five -= 3
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twenty += 1
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else:
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return False
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return True
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@ -106,22 +106,15 @@ class Solution {
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```python
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class Solution:
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def validMountainArray(self, arr: List[int]) -> bool:
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if len(arr) < 3 :
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return False
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i = 1
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flagIncrease = False # 上升
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flagDecrease = False # 下降
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while i < len(arr) and arr[i-1] < arr[i]:
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flagIncrease = True
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i += 1
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while i < len(arr) and arr[i-1] > arr[i]:
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flagDecrease = True
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i += 1
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return i == len(arr) and flagIncrease and flagDecrease
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left, right = 0, len(arr)-1
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while left < len(arr)-1 and arr[left+1] > arr[left]:
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left += 1
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while right > 0 and arr[right-1] > arr[right]:
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right -= 1
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return left == right and right != 0 and left != len(arr)-1
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```
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