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C/C++ Program for How to check if two given line segments intersect?

program solution

// A C++ program to check if two given line segments intersect 
#include <iostream> 
using namespace std; 

struct Point 

    int x; 
    int y; 
}; 

// Given three colinear points p, q, r, the function checks if point q lies on line segment 'pr' 
bool onSegment(Point p, Point q, Point r) 

    if (q.x <= max(p.x, r.x) && q.x >= min(p.x, r.x) &&q.y <= max(p.y, r.y) && q.y >= min(p.y, r.y)) 
    return true; 

    return false; 

// To find orientation of ordered triplet (p, q, r). 
// The function returns following values 
// 0 --> p, q and r are colinear 
// 1 --> Clockwise 
// 2 --> Counterclockwise 

int orientation(Point p, Point q, Point r) 

    int val = (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y); 

    if (val == 0) return 0; // colinear 

    return (val > 0)? 1: 2; // clock or counterclock wise 

// The main function that returns true if line segment 'p1q1' and 'p2q2' intersect. 
bool doIntersect(Point p1, Point q1, Point p2, Point q2) 

    // Find the four orientations needed for general and special cases 
    int o1 = orientation(p1, q1, p2); 
    int o2 = orientation(p1, q1, q2); 
    int o3 = orientation(p2, q2, p1); 
    int o4 = orientation(p2, q2, q1); 

    // General case 
    if (o1 != o2 && o3 != o4) 
        return true; 

    // Special Cases 
    // p1, q1 and p2 are colinear and p2 lies on segment p1q1 

    if (o1 == 0 && onSegment(p1, p2, q1)) return true; 

    // p1, q1 and q2 are colinear and q2 lies on segment p1q1 
    if (o2 == 0 && onSegment(p1, q2, q1)) return true; 

    // p2, q2 and p1 are colinear and p1 lies on segment p2q2 
    if (o3 == 0 && onSegment(p2, p1, q2)) return true; 

    // p2, q2 and q1 are colinear and q1 lies on segment p2q2 
    if (o4 == 0 && onSegment(p2, q1, q2)) return true; 

    return false; // Doesn't fall in any of the above cases 

// Driver program to test above functions 
int main() 

    struct Point p1 = {1, 1}, q1 = {10, 1}; 
    struct Point p2 = {1, 2}, q2 = {10, 2}; 

    doIntersect(p1, q1, p2, q2)? cout << "Yes\n": cout << "No\n"; 

    p1 = {10, 0}, q1 = {0, 10}; 
    p2 = {0, 0}, q2 = {10, 10}; 
    doIntersect(p1, q1, p2, q2)? cout << "Yes\n": cout << "No\n"; 

    p1 = {-5, -5}, q1 = {0, 0}; 
    p2 = {1, 1}, q2 = {10, 10}; 
    doIntersect(p1, q1, p2, q2)? cout << "Yes\n": cout << "No\n"; 

    return 0; 

 

Output

No

Yes

No