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| 1 | +class MaxFenwickTree: |
| 2 | + """ |
| 3 | + Maximum Fenwick Tree |
| 4 | +
|
| 5 | + More info: https://cp-algorithms.com/data_structures/fenwick.html |
| 6 | + --------- |
| 7 | + >>> ft = MaxFenwickTree(5) |
| 8 | + >>> ft.query(0, 5) |
| 9 | + 0 |
| 10 | + >>> ft.update(4, 100) |
| 11 | + >>> ft.query(0, 5) |
| 12 | + 100 |
| 13 | + >>> ft.update(4, 0) |
| 14 | + >>> ft.update(2, 20) |
| 15 | + >>> ft.query(0, 5) |
| 16 | + 20 |
| 17 | + >>> ft.update(4, 10) |
| 18 | + >>> ft.query(2, 5) |
| 19 | + 10 |
| 20 | + >>> ft.query(1, 5) |
| 21 | + 20 |
| 22 | + >>> ft.update(2, 0) |
| 23 | + >>> ft.query(0, 5) |
| 24 | + 10 |
| 25 | + >>> ft = MaxFenwickTree(10000) |
| 26 | + >>> ft.update(255, 30) |
| 27 | + >>> ft.query(0, 10000) |
| 28 | + 30 |
| 29 | + """ |
| 30 | + |
| 31 | + def __init__(self, size: int) -> None: |
| 32 | + """ |
| 33 | + Create empty Maximum Fenwick Tree with specified size |
| 34 | +
|
| 35 | + Parameters: |
| 36 | + size: size of Array |
| 37 | +
|
| 38 | + Returns: |
| 39 | + None |
| 40 | + """ |
| 41 | + self.size = size |
| 42 | + self.arr = [0] * size |
| 43 | + self.tree = [0] * size |
| 44 | + |
| 45 | + @staticmethod |
| 46 | + def get_next(index: int) -> int: |
| 47 | + """ |
| 48 | + Get next index in O(1) |
| 49 | + """ |
| 50 | + return index + (index & -index) |
| 51 | + |
| 52 | + @staticmethod |
| 53 | + def get_prev(index: int) -> int: |
| 54 | + """ |
| 55 | + Get previous index in O(1) |
| 56 | + """ |
| 57 | + return index - (index & -index) |
| 58 | + |
| 59 | + def update(self, index: int, value: int) -> None: |
| 60 | + """ |
| 61 | + Set index to value in O(lg^2 N) |
| 62 | +
|
| 63 | + Parameters: |
| 64 | + index: index to update |
| 65 | + value: value to set |
| 66 | +
|
| 67 | + Returns: |
| 68 | + None |
| 69 | + """ |
| 70 | + self.arr[index] = value |
| 71 | + while index < self.size: |
| 72 | + self.tree[index] = max(value, self.query(self.get_prev(index), index)) |
| 73 | + index = self.get_next(index) |
| 74 | + |
| 75 | + def query(self, left: int, right: int) -> int: |
| 76 | + """ |
| 77 | + Answer the query of maximum range [l, r) in O(lg^2 N) |
| 78 | +
|
| 79 | + Parameters: |
| 80 | + left: left index of query range (inclusive) |
| 81 | + right: right index of query range (exclusive) |
| 82 | +
|
| 83 | + Returns: |
| 84 | + Maximum value of range [left, right) |
| 85 | + """ |
| 86 | + right -= 1 # Because of right is exclusive |
| 87 | + result = 0 |
| 88 | + while left < right: |
| 89 | + current_left = self.get_prev(right) |
| 90 | + if left < current_left: |
| 91 | + result = max(result, self.tree[right]) |
| 92 | + right = current_left |
| 93 | + else: |
| 94 | + result = max(result, self.arr[right]) |
| 95 | + right -= 1 |
| 96 | + return result |
| 97 | + |
| 98 | + |
| 99 | +if __name__ == "__main__": |
| 100 | + import doctest |
| 101 | + |
| 102 | + doctest.testmod() |
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