From ed3cc974ba2a85c32625319bdb52fa972659c97f Mon Sep 17 00:00:00 2001
From: mahammadhussain98 <141554718+mahammadhussain98@users.noreply.github.com>
Date: Sun, 1 Oct 2023 23:39:46 +0530
Subject: [PATCH] Added Chazelle's Algorithm for Closest Pair Problem

Details:
- Added the implementation of Chazelle's Algorithm in C++.
- This algorithm efficiently finds the closest pair of points in the Euclidean plane.
- Incorporated user input for point coordinates in the format "1,2,3...".
- The algorithm uses a divide-and-conquer approach to optimize the closest pair search.
- Included detailed documentation for the algorithm's usage and functionality.

Usage:
- Run the program, specifying the number of points and their coordinates as input.
- The program will calculate and display the closest pair of points along with their Euclidean distance.
---
 divide_and_conquer/Chazelle's Algorithm.cpp | 114 ++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 divide_and_conquer/Chazelle's Algorithm.cpp

diff --git a/divide_and_conquer/Chazelle's Algorithm.cpp b/divide_and_conquer/Chazelle's Algorithm.cpp
new file mode 100644
index 000000000..5b73c5975
--- /dev/null
+++ b/divide_and_conquer/Chazelle's Algorithm.cpp	
@@ -0,0 +1,114 @@
+#include <iostream>
+#include <vector>
+#include <cmath>
+#include <algorithm>
+#include <sstream>
+
+using namespace std;
+
+// Data structure to represent a point in 2D space
+struct Point {
+    double x, y;
+
+    // Constructor to initialize a point
+    Point(double x, double y) : x(x), y(y) {}
+};
+
+// Data structure to represent an edge between two points
+struct Edge {
+    int u, v;
+    double weight;
+
+    // Constructor to initialize an edge
+    Edge(int u, int v, double weight) : u(u), v(v), weight(weight) {}
+};
+
+// Function to calculate the Euclidean distance between two points
+double euclideanDistance(const Point& p1, const Point& p2) {
+    double dx = p1.x - p2.x;
+    double dy = p1.y - p2.y;
+    return sqrt(dx * dx + dy * dy);
+}
+
+// Function to find the closest pair of points in a given range
+Edge closestPair(vector<Point>& points, int left, int right) {
+    if (right - left <= 1) {
+        // Base case: if there are only two points, return the edge between them
+        return Edge(left, right, euclideanDistance(points[left], points[right]));
+    }
+
+    // Divide the range into two halves
+    int mid = (left + right) / 2;
+    double midX = points[mid].x;
+
+    // Recursively find the closest pair in the left and right halves
+    Edge leftClosest = closestPair(points, left, mid);
+    Edge rightClosest = closestPair(points, mid + 1, right);
+
+    // Find the minimum of the two closest pairs
+    Edge minClosest = (leftClosest.weight < rightClosest.weight) ? leftClosest : rightClosest;
+
+    // Create a vector to store points in the strip of width 2*minClosest.weight
+    vector<Point> strip;
+
+    // Populate the strip with points whose x-coordinate is within the strip
+    for (int i = left; i <= right; i++) {
+        if (abs(points[i].x - midX) < minClosest.weight) {
+            strip.push_back(points[i]);
+        }
+    }
+
+    // Sort the points in the strip by their y-coordinates
+    sort(strip.begin(), strip.end(), [](const Point& p1, const Point& p2) {
+        return p1.y < p2.y;
+    });
+
+    // Iterate through the strip to find potential closer pairs
+    for (int i = 0; i < strip.size(); i++) {
+        for (int j = i + 1; j < strip.size() && (strip[j].y - strip[i].y) < minClosest.weight; j++) {
+            double distance = euclideanDistance(strip[i], strip[j]);
+            if (distance < minClosest.weight) {
+                minClosest = Edge(left + i, left + j, distance);
+            }
+        }
+    }
+
+    return minClosest;
+}
+
+int main() {
+    int n; // Number of points
+    cout << "Enter the number of points: ";
+    cin >> n;
+    cin.ignore(); // Consume the newline character
+
+    vector<Point> points;
+    cout << "Enter the coordinates of each point (comma-separated):" << endl;
+    
+    // Read the coordinates as a single comma-separated string
+    string coordinates;
+    getline(cin, coordinates);
+
+    // Use a stringstream to parse the coordinates
+    stringstream ss(coordinates);
+    for (int i = 0; i < n; i++) {
+        double x, y;
+        char comma;
+        ss >> x >> comma >> y;
+        points.push_back(Point(x, y));
+    }
+
+    // Sort the points by their x-coordinates
+    sort(points.begin(), points.end(), [](const Point& p1, const Point& p2) {
+        return p1.x < p2.x;
+    });
+
+    // Find the closest pair of points using Chazelle's Algorithm
+    Edge closest = closestPair(points, 0, n - 1);
+
+    cout << "Closest pair of points: (" << points[closest.u].x << ", " << points[closest.u].y << ") and ("
+         << points[closest.v].x << ", " << points[closest.v].y << ")" << endl;
+    cout << "Distance between them: " << closest.weight << endl;
+
+    return 0;
+}