Implement closest pair of points algorithm

Author: sandeepgoudmacha

src/main/java/com/thealgorithms/geometry/closestPairOfPoints.java

@@ -0,0 +1,48 @@
+package com.thealgorithms.geometry;
+
+import java.util.*;
+
+public final class ClosestPairOfPoints {
+    private ClosestPairOfPoints() {}
+
+    public static double closestPair(List<Point> points) {
+        List<Point> sortedByX = new ArrayList<>(points);
+        sortedByX.sort(Comparator.comparingDouble(p -> p.x));
+        return divide(sortedByX);
+    }
+
+    private static double divide(List<Point> pts) {
+        int n = pts.size();
+        if (n <= 3) return bruteForce(pts);
+
+        int mid = n / 2;
+        Point midPoint = pts.get(mid);
+
+        double dl = divide(pts.subList(0, mid));
+        double dr = divide(pts.subList(mid, n));
+        double d = Math.min(dl, dr);
+
+        List<Point> strip = new ArrayList<>();
+        for (Point p : pts) {
+            if (Math.abs(p.x - midPoint.x) < d) strip.add(p);
+        }
+
+        strip.sort(Comparator.comparingDouble(p -> p.y));
+        for (int i = 0; i < strip.size(); ++i) {
+            for (int j = i + 1; j < strip.size() && (strip.get(j).y - strip.get(i).y) < d; ++j) {
+                d = Math.min(d, strip.get(i).distance(strip.get(j)));
+            }
+        }
+        return d;
+    }
+
+    private static double bruteForce(List<Point> pts) {
+        double min = Double.POSITIVE_INFINITY;
+        for (int i = 0; i < pts.size(); ++i) {
+            for (int j = i + 1; j < pts.size(); ++j) {
+                min = Math.min(min, pts.get(i).distance(pts.get(j)));
+            }
+        }
+        return min;
+    }
+}