implement segment tree

CMakeLists.txt

@@ -5,6 +5,6 @@ set(CMAKE_CXX_STANDARD 20)
 
 find_package(benchmark REQUIRED)
 
-add_executable(prog main.cpp segment_tree.h geometry.h)
+add_executable(prog main.cpp segment_tree.h geometry.h segment_tree.cpp)
 
 target_link_libraries(prog benchmark::benchmark)

geometry.h

@@ -21,4 +21,22 @@ struct Interval {
     Coordinate right;
 };
 
+struct Rectangle {
+    Point bottom_left;
+    Point top_right;
+
+    // only for algorithm
+    Index i_left;
+    Index i_right;
+};
+
+struct RectCoord {
+    Coordinate coord;
+    Rectangle* rect; // guaranteed to be valid at all times
+    bool operator<(const RectCoord &other) {
+        return coord < other.coord;
+    }
+};
+
+
 #endif //PROG_GEOMETRY_H

main.cpp

@@ -5,22 +5,6 @@
 
 #include "geometry.h"
 
-struct Rectangle {
-    Point bottom_left;
-    Point top_right;
-
-    // only for algorithm
-    Index i_left;
-    Index i_right;
-};
-
-struct RectCoord {
-    Coordinate coord;
-    Rectangle* rect; // guaranteed to be valid at all times
-    bool operator<(const RectCoord &other) {
-        return coord < other.coord;
-    }
-};
 
 Unit get_area_union(std::vector<Rectangle> rectangles) {
     // do some input sanity checks

segment_tree.cpp

@@ -0,0 +1,64 @@
+//
+// Created by maximilian on 16.04.22.
+//
+#include <assert.h>
+#include <bit>
+#include "segment_tree.h"
+
+SegmentTree::SegmentTree(const std::vector<RectCoord> &coords):
+    _covered_cross_section_length(0), _nodes() {
+
+    assert(!coords.empty());
+
+    // reserve nodes for a full binary tree with at least as many leaves as intervals
+    size_t num_leaf_nodes = coords.size() -1;
+    size_t num_meta_nodes = std::bit_ceil(num_leaf_nodes) - 1;
+
+    // Initialize all nodes with zero coverage and dummy interval
+    _nodes.resize(2 * num_meta_nodes - 1, {0, coords[num_leaf_nodes].coord, coords[num_leaf_nodes].coord});
+
+    // We initialize the tree from bottom up, keeping track of the index ranges
+    // and the length of the corresponding segment
+
+    for(Index leaf_node_idx = 0 ; leaf_node_idx < num_leaf_nodes ; ++leaf_node_idx) {
+        _nodes[leaf_node_idx + num_meta_nodes].left_coord = coords[leaf_node_idx].coord;
+        _nodes[leaf_node_idx + num_meta_nodes].right_coord = coords[leaf_node_idx +1].coord;
+    }
+    // Note that there are remaining leafs that represent dummy ranges
+    for(Index node_idx = num_meta_nodes - 1; node_idx >= 0; ++node_idx) {
+        _nodes[node_idx].left_coord = left_child(node_idx).left_coord;
+        _nodes[node_idx].right_coord = right_child(node_idx).right_coord;
+    }
+
+    assert(_nodes.front().left_coord == coords.front().coord);
+    assert(_nodes.front().right_coord == coords.back().coord);
+    assert(_nodes.front().segment_length() == coords.back().coord - coords.front().coord);
+}
+
+void SegmentTree::add_interval(Interval interval, Index node_idx) {
+    if (interval.left <= _nodes[node_idx].left_coord && _nodes[node_idx].right_coord <= interval.right) {
+        update_added(node_idx);
+    } else {
+        if(interval.left < left_child(node_idx).right_coord) {
+            add_interval(interval, left_child_idx(node_idx));
+        }
+        if(right_child(node_idx).left_coord < interval.right) {
+            add_interval(interval, right_child_idx(node_idx));
+        }
+    }
+}
+
+void SegmentTree::remove_interval(Interval interval, Index node_idx) {
+    if (interval.left <= _nodes[node_idx].left_coord && _nodes[node_idx].right_coord <= interval.right) {
+        update_removed(node_idx);
+    } else {
+        if(interval.left < left_child(node_idx).right_coord) {
+            remove_interval(interval, left_child_idx(node_idx));
+        }
+        if(right_child(node_idx).left_coord < interval.right) {
+            remove_interval(interval, right_child_idx(node_idx));
+        }
+    }
+}
+
+

segment_tree.h

@@ -9,13 +9,92 @@
 #define PROG_SEGMENT_TREE_H
 
 
-class SegmentTree {
-    SegmentTree(const std::vector<Coordinate>);
-
-    Unit length_covered_intervals();
-
-    void add_interval(Interval interval);
-    void remove_interval(Interval interval);
+struct TreeNode {
+    unsigned coverage;
+    Coordinate left_coord;
+    Coordinate right_coord;
+    inline Unit segment_length();
 };
 
+
+class SegmentTree {
+    std::vector<TreeNode> _nodes;
+    Unit _covered_cross_section_length;
+public:
+    /**
+     *
+     * @param coords Sorted vector of coordinates
+     */
+    SegmentTree(const std::vector<RectCoord>& coords);
+
+    inline Unit length_covered_intervals();
+    inline void add_interval(Interval interval);
+    inline void remove_interval(Interval interval);
+
+private:
+    inline static Index left_child_idx(Index node_idx);
+    inline static Index right_child_idx(Index node_idx);
+    inline TreeNode& left_child(Index node_idx);
+    inline TreeNode& right_child(Index node_idx);
+    inline void update_added(Index node_idx);
+    inline void update_removed(Index node_idx);
+    void add_interval(Interval interval, Index node_idx);
+    void remove_interval(Interval interval, Index node_idx);
+
+};
+
+/*****************************************************
+ * INLINE section
+ ****************************************************/
+
+
+
+TreeNode& SegmentTree::left_child(Index node_idx) {
+    return _nodes[left_child_idx(node_idx)];
+}
+
+TreeNode& SegmentTree::right_child(Index node_idx) {
+    return _nodes[right_child_idx(node_idx)];
+}
+
+Unit SegmentTree::length_covered_intervals() {
+    return _covered_cross_section_length;
+}
+
+void SegmentTree::add_interval(Interval interval) {
+    add_interval(interval, 0);
+}
+
+void SegmentTree::remove_interval(Interval interval) {
+    remove_interval(interval, 0);
+}
+
+void SegmentTree::update_added(Index node_idx) {
+    ++(_nodes[node_idx].coverage);
+    if(_nodes[node_idx].coverage == 1) {
+        _covered_cross_section_length += _nodes[node_idx].segment_length();
+    }
+}
+
+void SegmentTree::update_removed(Index node_idx) {
+    --(_nodes[node_idx].coverage);
+    if(_nodes[node_idx].coverage == 0) {
+        _covered_cross_section_length -= _nodes[node_idx].segment_length();
+    }
+}
+
+Index SegmentTree::left_child_idx(Index node_idx) {
+    return 2*node_idx + 1;
+}
+
+Index SegmentTree::right_child_idx(Index node_idx) {
+    return 2*node_idx + 2;
+}
+
+
+Unit TreeNode::segment_length() {
+    return right_coord - left_coord;
+}
+
+
 #endif //PROG_SEGMENT_TREE_H