implement segment tree using node (new .py file in data_structures/binary_tree/segment_tree_node.py)

data_structures/binary_tree/segment_tree_node.py

@@ -0,0 +1,185 @@
+class Node:
+    def __init__(self, start: int, end: int) -> None:
+        # Initializes a segment tree node with start and end indices
+        self.start = start
+        self.end = end
+        self.value: int = 0
+        self.left: Node = self
+        self.right: Node = self
+
+
+class SegmentTree:
+    def __init__(self, nums: list[int], mode: str = "max") -> None:
+        """
+        Initializes the Segment Tree.
+        :param nums: List of integers to build the tree from.
+        :param mode: Operation mode of the tree ('max' or 'sum').
+        """
+        self.size = len(nums)
+        self.mode = mode
+        if mode not in {"max", "sum"}:
+            self.mode = "max"  # Default to max if invalid mode is given
+
+        # Build the tree from the input list
+        self.root: Node = self.build(0, self.size - 1, nums)
+
+    def build(self, start: int, end: int, nums: list[int]) -> Node:
+        """
+        Recursively builds the segment tree.
+        :param start: Start index of the segment.
+        :param end: End index of the segment.
+        :param nums: Original input array.
+        :return: Root node of the constructed subtree.
+
+        >>> tree = SegmentTree([1, 2, 3, 4, 5], mode="max")
+        >>> tree.root.value
+        5
+        """
+        if start > end:
+            return Node(0, 0)
+
+        if start == end:
+            # Leaf node
+            n = Node(start, end)
+            n.value = nums[start]
+            return n
+
+        mid = (start + end) // 2
+        root = Node(start, end)
+        root.left = self.build(start, mid, nums)
+        root.right = self.build(mid + 1, end, nums)
+
+        # Set the value according to the mode
+        if self.mode == "max":
+            root.value = max(root.left.value, root.right.value)
+        else:
+            root.value = root.left.value + root.right.value
+
+        return root
+
+    def max_in_range(self, start_index: int, end_index: int) -> int:
+        """
+        Queries the maximum value in a given range.
+        Only works in 'max' mode.
+
+        >>> tree = SegmentTree([1, 2, 3, 4, 5], mode="max")
+        >>> tree.max_in_range(1, 3)
+        4
+        """
+        if self.mode == "sum":
+            raise Exception("Current Segment Tree doesn't support finding max")
+
+        if start_index > end_index or start_index < 0 or end_index >= self.size:
+            raise Exception("Invalid index")
+
+        if self.root is None:
+            raise ValueError("Tree not initialized")
+
+        return self.query(self.root, start_index, end_index, 0, self.size - 1)
+
+    def sum_in_range(self, start_index: int, end_index: int) -> int:
+        """
+        Queries the sum of values in a given range.
+        Only works in 'sum' mode.
+
+        >>> tree = SegmentTree([1, 2, 3, 4, 5], mode="sum")
+        >>> tree.sum_in_range(1, 3)
+        9
+        """
+        if self.mode == "max":
+            raise Exception("Current Segment Tree doesn't support summing")
+
+        if start_index > end_index or start_index < 0 or end_index >= self.size:
+            raise Exception("Invalid index")
+
+        if self.root is None:
+            raise ValueError("Tree not initialized")
+
+        return self.query(self.root, start_index, end_index, 0, self.size - 1)
+
+    def query(
+        self, node: Node, start_index: int, end_index: int, start: int, end: int
+    ) -> int:
+        """
+        Recursively queries a value (max or sum) in a given range.
+        :param node: Current node in the tree.
+        :param start_index: Query start index.
+        :param end_index: Query end index.
+        :param start: Node's segment start.
+        :param end: Node's segment end.
+        :return: Result of query in the range.
+
+        >>> tree = SegmentTree([1, 2, 3, 4, 5], mode="max")
+        >>> tree.query(tree.root, 1, 3, 0, 4)
+        4
+        """
+        # Complete overlap
+        if start_index <= start and end <= end_index:
+            return node.value
+
+        mid = (start + end) // 2
+
+        if end_index <= mid:
+            # Entire range is in the left child
+            return self.query(node.left, start_index, end_index, start, mid)
+        elif start_index > mid:
+            # Entire range is in the right child
+            return self.query(node.right, start_index, end_index, mid + 1, end)
+        elif self.mode == "max":
+            return max(
+                self.query(node.left, start_index, end_index, start, mid),
+                self.query(node.right, start_index, end_index, mid + 1, end),
+            )
+        else:
+            return self.query(
+                node.left, start_index, end_index, start, mid
+            ) + self.query(node.right, start_index, end_index, mid + 1, end)
+
+    def update(self, index: int, new_value: int) -> None:
+        """
+        Updates a value at a specific index in the segment tree.
+        :param index: Index to update.
+        :param new_value: New value to set.
+
+        >>> tree = SegmentTree([1, 2, 3, 4, 5], mode="max")
+        >>> tree.update(2, 6)
+        >>> tree.max_in_range(1, 3)
+        6
+        """
+        if index < 0 or index >= self.size:
+            raise Exception("Invalid index")
+
+        self.modify(self.root, index, new_value, 0, self.size - 1)
+
+    def modify(
+        self, node: Node, index: int, new_value: int, start: int, end: int
+    ) -> None:
+        """
+        Recursively updates the tree to reflect a change at a specific index.
+        :param node: Current node being processed.
+        :param index: Index to update.
+        :param new_value: New value to assign.
+        :param start: Start index of node's segment.
+        :param end: End index of node's segment.
+
+        >>> tree = SegmentTree([1, 2, 3, 4, 5], mode="max")
+        >>> tree.modify(tree.root, 2, 6, 0, 4)
+        >>> tree.max_in_range(0, 4)
+        6
+        """
+        if start == end:
+            node.value = new_value
+            return
+
+        mid = (start + end) // 2
+
+        if index <= mid:
+            self.modify(node.left, index, new_value, start, mid)
+        else:
+            self.modify(node.right, index, new_value, mid + 1, end)
+
+        # Recompute current node's value after update
+        if self.mode == "max":
+            node.value = max(node.left.value, node.right.value)
+        else:
+            node.value = node.left.value + node.right.value