[Convex packet Graham_Scan algorithm] HDU 1348 Wall

Typical convex bag question: Calculate the perimeter of the peripheral wall

 

C ++ code

# Include <iostream>

# Include <fstream>

# Include <algorithm>

# Include <string>

# Include <set>

// # Include <map>

# Include <queue>

# Include <utility>

# Include <stack>

# Include <list>

# Include <vector>

# Include <cstdio>

# Include <cstdlib>

# Include <cstring>

# Include <cmath>

# Include <ctime>

# Include <ctype. h>

Using namespace std;

# Define PI 3.14159265

 

Struct point {

Double x, y, angel;

} P [1, 1005], ch [2, 1005];

 

Double dist (point a, point B)

{

Return sqrt (a. x-b.x) * (a. x-b.x) + (a. y-b.y) * (a. y-b.y ));

}

 

Double multi (point a, point B, point c)

{

Double x1, y1, x2, y2;

X1 = B. x-a. x;

Y1 = B. y-a. y;

X2 = c. x-B. x;

Y2 = c. y-B. y;

Return x1 * y2-x2 * y1;

}

 

Bool cmp (point a, point B)

{

If (a. y = B. y)

Return a. x <B. x;

Return a. y <B. y;

}

 

Bool cmp2 (point a, point B)

{

If (a. angel = B. angel)

{

If (a. x = B. x)

Return a. y> B. y;

Return a. x> B. x;

}

Return a. angel <B. angel;

}

 

Int main ()

{

Int n, I, top, t;

Double r, len;

Scanf ("% d", & t );

While (t --)

{

Scanf ("% d % lf", & n, & r );

For (I = 0; I <n; I ++)

Scanf ("% lf", & p [I]. x, & p [I]. y );

Sort (p, p + n, cmp); // locate p [0] in the lower left corner.

 

// Locate the polar angle relative to p [0] and sort the vertices except p [0] According to the Polar Angle

For (I = 1; I <n; I ++)

P [I]. angel = atan2 (p [I]. y-p [0]. y, p [I]. x-p [0]. x );

Sort (p + 1, p + n, cmp2 );

 

// Graham_Scan Algorithm

Ch [0] = p [0], ch [1] = p [1], ch [2] = p [2];

Top = 3;

For (I = 3; I <n; I ++)

{

While (top> 2 & multi (ch [top-2], ch [top-1], p [I]) <= 0)

Top --;

Ch [top ++] = p [I];

}

 

// Calculate the perimeter

Len = dist (ch [0], ch [top-1]);

For (I = 1; I <top; I ++)

Len + = dist (ch [I], ch [I-1]);

Len + = 2 * PI * r; // Add an arc to the circle!

 

Printf ("%. 0lf \ n", len );

If (t)

Printf ("\ n ");

}

Return 0;

}