85 lines
2.5 KiB
C++
85 lines
2.5 KiB
C++
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/*This is a C++ Program to implement Jarvis March to find convex hull. The idea of Jarvis’s Algorithm is simple, we start from the leftmost point (or point with minimum x coordinate value) and we keep wrapping points in counterclockwise direction.*/
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// A C++ program to find convex hull of a set of points
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// Refer http://www.geeksforgeeks.org/check-if-two-given-line-segments-intersect/
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// for explanation of orientation()
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#include <iostream>
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using namespace std;
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// Define Infinite (Using INT_MAX caused overflow problems)
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#define INF 10000
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struct Point
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{
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int x;
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int y;
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};
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// To find orientation of ordered triplet (p, q, r).
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// The function returns following values
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// 0 --> p, q and r are colinear
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// 1 --> Clockwise
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// 2 --> Counterclockwise
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int orientation(Point p, Point q, Point r)
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{
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int val = (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
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if (val == 0)
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return 0; // colinear
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return (val > 0) ? 1 : 2; // clock or counterclock wise
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}
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// Prints convex hull of a set of n points.
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void convexHull(Point points[], int n)
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{
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// There must be at least 3 points
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if (n < 3)
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return;
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// Initialize Result
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int next[n];
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for (int i = 0; i < n; i++)
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next[i] = -1;
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// Find the leftmost point
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int l = 0;
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for (int i = 1; i < n; i++)
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if (points[i].x < points[l].x)
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l = i;
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// Start from leftmost point, keep moving counterclockwise
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// until reach the start point again
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int p = l, q;
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do
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{
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// Search for a point 'q' such that orientation(p, i, q) is
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// counterclockwise for all points 'i'
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q = (p + 1) % n;
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for (int i = 0; i < n; i++)
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if (orientation(points[p], points[i], points[q]) == 2)
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q = i;
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next[p] = q; // Add q to result as a next point of p
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p = q; // Set p as q for next iteration
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}
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while (p != l);
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// Print Result
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for (int i = 0; i < n; i++)
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{
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if (next[i] != -1)
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cout << "(" << points[i].x << ", " << points[i].y << ")\n";
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}
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}
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// Driver program to test above functions
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int main()
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{
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Point points[] = { { 0, 3 }, { 2, 2 }, { 1, 1 }, { 2, 1 }, { 3, 0 },
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{ 0, 0 }, { 3, 3 }
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};
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cout << "The points in the convex hull are: ";
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int n = sizeof(points) / sizeof(points[0]);
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convexHull(points, n);
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return 0;
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}
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/*
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The points in the convex hull are: (0, 3)
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(3, 0)
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(0, 0)
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(3, 3)
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