Merge pull request #286 from asifsadek/master

graham_scan

Author: probot-auto-merge[bot]

graham_scan.cpp

@@ -0,0 +1,80 @@
+
+
+#include <iostream>
+#include <algorithm>
+#include <vector>
+using namespace std;
+
+struct point
+{
+    double x, y;
+    point(double x, double y) : x(x), y(y)
+    {
+    }
+    point()
+    {
+    }
+};
+
+// custom compare for sorting points
+bool cmp(point a, point b)
+{
+    return a.x < b.x || (a.x == b.x && a.y < b.y);
+}
+
+// check clockwise orientation of points
+bool cw(point a, point b, point c)
+{
+    return a.x * (b.y - c.y) + b.x * (c.y - a.y) + c.x * (a.y - b.y) < 0;
+}
+
+// check counter-clockwise orientation of points
+bool ccw(point a, point b, point c)
+{
+    return a.x * (b.y - c.y) + b.x * (c.y - a.y) + c.x * (a.y - b.y) > 0;
+}
+
+// graham scan with Andrew improvements
+void convex_hull(vector<point> &points)
+{
+    if (points.size() == 1)
+        return;
+    sort(points.begin(), points.end(), &cmp);
+    point p1 = points[0], p2 = points.back();
+    vector<point> up, down;
+    up.push_back(p1);
+    down.push_back(p1);
+    for (size_t i = 1; i < points.size(); ++i)
+    {
+        if (i == points.size() - 1 || cw(p1, points[i], p2))
+        {
+            while (up.size() >= 2 && !cw(up[up.size() - 2], up[up.size() - 1], points[i]))
+                up.pop_back();
+            up.push_back(points[i]);
+        }
+        if (i == points.size() - 1 || ccw(p1, points[i], p2))
+        {
+            while (down.size() >= 2 &&
+                   !ccw(down[down.size() - 2], down[down.size() - 1], points[i]))
+                down.pop_back();
+            down.push_back(points[i]);
+        }
+    }
+    cout << "Convex hull is:" << endl;
+    for (size_t i = 0; i < up.size(); ++i)
+        cout << "x: " << up[i].x << " y: " << up[i].y << endl;
+    for (int i = down.size() - 2; i > 0; --i)
+        cout << "x: " << down[i].x << " y: " << down[i].y << endl;
+}
+
+int main()
+{
+    int n;
+    cout << "Enter number of points followed by points" << endl;
+    cin >> n;
+    vector<point> points(n);
+    for (int i = 0; i < n; i++)
+        cin >> points[i].x >> points[i].y;
+    convex_hull(points);
+    return 0;
+}