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Fix Max Fenwick Tree #6328

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Merged
merged 1 commit into from
Sep 14, 2022
Merged

Fix Max Fenwick Tree #6328

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24 changes: 18 additions & 6 deletions data_structures/binary_tree/maximum_fenwick_tree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ class MaxFenwickTree:
20
>>> ft.update(4, 10)
>>> ft.query(2, 5)
10
20
>>> ft.query(1, 5)
20
>>> ft.update(2, 0)
Expand All @@ -26,6 +26,14 @@ class MaxFenwickTree:
>>> ft.update(255, 30)
>>> ft.query(0, 10000)
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:
Expand All @@ -47,14 +55,14 @@ def get_next(index: int) -> int:
"""
Get next index in O(1)
"""
return index + (index & -index)
return index | (index + 1)

@staticmethod
def get_prev(index: int) -> int:
"""
Get previous index in O(1)
"""
return index - (index & -index)
return (index & (index + 1)) - 1

def update(self, index: int, value: int) -> None:
"""
Expand All @@ -69,7 +77,11 @@ def update(self, index: int, value: int) -> None:
"""
self.arr[index] = value
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)

def query(self, left: int, right: int) -> int:
Expand All @@ -85,9 +97,9 @@ def query(self, left: int, right: int) -> int:
"""
right -= 1 # Because of right is exclusive
result = 0
while left < right:
while left <= right:
current_left = self.get_prev(right)
if left < current_left:
if left <= current_left:
result = max(result, self.tree[right])
right = current_left
else:
Expand Down