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Fix Max Fenwick Tree (#6328)

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C21 2022-09-14 13:54:55 +05:30 committed by GitHub
parent 4e4fe95369
commit 81e30fd33c
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1 changed files with 18 additions and 6 deletions
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24
data_structures/binary_tree/maximum_fenwick_tree.py
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@ -16,7 +16,7 @@ class MaxFenwickTree:
20 20
>>> ft.update(4, 10) >>> ft.update(4, 10)
>>> ft.query(2, 5) >>> ft.query(2, 5)
10 20
>>> ft.query(1, 5) >>> ft.query(1, 5)
20 20
>>> ft.update(2, 0) >>> ft.update(2, 0)
@ -26,6 +26,14 @@ class MaxFenwickTree:
>>> ft.update(255, 30) >>> ft.update(255, 30)
>>> ft.query(0, 10000) >>> ft.query(0, 10000)
30 30
>>> ft = MaxFenwickTree(6)
>>> ft.update(5, 1)
>>> ft.query(5, 6)
1
>>> ft = MaxFenwickTree(6)
>>> ft.update(0, 1000)
>>> ft.query(0, 1)
1000
""" """
def __init__(self, size: int) -> None: def __init__(self, size: int) -> None:
@ -47,14 +55,14 @@ class MaxFenwickTree:
""" """
Get next index in O(1) Get next index in O(1)
""" """
return index + (index & -index) return index | (index + 1)
@staticmethod @staticmethod
def get_prev(index: int) -> int: def get_prev(index: int) -> int:
""" """
Get previous index in O(1) Get previous index in O(1)
""" """
return index - (index & -index) return (index & (index + 1)) - 1
def update(self, index: int, value: int) -> None: def update(self, index: int, value: int) -> None:
""" """
@ -69,7 +77,11 @@ class MaxFenwickTree:
""" """
self.arr[index] = value self.arr[index] = value
while index < self.size: while index < self.size:
self.tree[index] = max(value, self.query(self.get_prev(index), index)) current_left_border = self.get_prev(index) + 1
if current_left_border == index:
self.tree[index] = value
else:
self.tree[index] = max(value, current_left_border, index)
index = self.get_next(index) index = self.get_next(index)
def query(self, left: int, right: int) -> int: def query(self, left: int, right: int) -> int:
@ -85,9 +97,9 @@ class MaxFenwickTree:
""" """
right -= 1 # Because of right is exclusive right -= 1 # Because of right is exclusive
result = 0 result = 0
while left < right: while left <= right:
current_left = self.get_prev(right) current_left = self.get_prev(right)
if left < current_left: if left <= current_left:
result = max(result, self.tree[right]) result = max(result, self.tree[right])
right = current_left right = current_left
else: else: