72 lines
1.9 KiB
Java
72 lines
1.9 KiB
Java
// https://en.wikipedia.org/wiki/Quadtree
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public class QuadTree {
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static class Node {
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int count;
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Node topLeft, topRight, bottomLeft, bottomRight;
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}
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Node root;
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static final int maxx = (1 << 30);
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static final int maxy = (1 << 30);
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// insert point (x,y)
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public void insert(int x, int y) {
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root = insert(root, 0, 0, maxx - 1, maxy - 1, x, y);
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}
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Node insert(Node node, int ax, int ay, int bx, int by, int x, int y) {
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if (ax > x || x > bx || ay > y || y > by)
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return node;
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if (node == null)
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node = new Node();
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++node.count;
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if (ax == bx && ay == by)
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return node;
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int mx = (ax + bx) >> 1;
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int my = (ay + by) >> 1;
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node.bottomLeft = insert(node.bottomLeft, ax, ay, mx, my, x, y);
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node.topLeft = insert(node.topLeft, ax, my + 1, mx, by, x, y);
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node.bottomRight = insert(node.bottomRight, mx + 1, ay, bx, my, x, y);
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node.topRight = insert(node.topRight, mx + 1, my + 1, bx, by, x, y);
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return node;
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}
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// number of points in [x1,x2] x [y1,y2]
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public int count(int x1, int y1, int x2, int y2) {
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return count(root, 0, 0, maxx - 1, maxy - 1, x1, y1, x2, y2);
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}
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int count(Node node, int ax, int ay, int bx, int by, int x1, int y1, int x2, int y2) {
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if (node == null || ax > x2 || x1 > bx || ay > y2 || y1 > by)
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return 0;
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if (x1 <= ax && bx <= x2 && y1 <= ay && by <= y2)
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return node.count;
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int mx = (ax + bx) >> 1;
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int my = (ay + by) >> 1;
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int res = 0;
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res += count(node.bottomLeft, ax, ay, mx, my, x1, y1, x2, y2);
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res += count(node.topLeft, ax, my + 1, mx, by, x1, y1, x2, y2);
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res += count(node.bottomRight, mx + 1, ay, bx, my, x1, y1, x2, y2);
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res += count(node.topRight, mx + 1, my + 1, bx, by, x1, y1, x2, y2);
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return res;
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}
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// Usage example
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public static void main(String[] args) {
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QuadTree t = new QuadTree();
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t.insert(0, 0);
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t.insert(1, 0);
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t.insert(2, 0);
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t.insert(3, 0);
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System.out.println(4 == t.count(0, 0, 3, 0));
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}
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}
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