Nyoj 78 ring pool (Entry level convex hull)

Link: nyoj 78

Question: This question is mainly about the usage of convex hull. It is an entry level. Of course, the premise is that you have been in touch with the plane ry:

AC code:

1 # include <iostream> 2 # include <algorithm> 3 # include <cstdio> 4 # include <cstring> 5 # include <vector> 6 using namespace STD; 7 struct T 8 {9 int X, Y; 10 friend int operator <(t a, t B) 11 {12 if (. x <B. x) | (. X = B. X &. Y <B. y) 13 return 1; 14 return 0; 15} 16} A [105], ANS [105]; 17 // used to judge whether the Left or Right side of the line formed by the third point is the current two points, and the return value on the right is less than 0; 18 double judge (t a, t B, t C) 19 {20 return (B. x-a.x) * (C. y-a.y)-(C. x-a.x) * (B. y-a.y); 21} 22 int main () 23 {24 int T, M; 25 scanf ("% d", & T); 26 while (t --) 27 {28 29 scanf ("% d", & M); 30 for (INT I = 0; I <m; I ++) 31 {32 scanf ("% d", & A [I]. x, & A [I]. y); 33} 34 sort (A, A + M); 35 int k1 = 0; 36 for (INT I = 0; I <m; I ++) // lower convex hull, scanning points from below; 37 {38 While (K1> 1 & judge (ANS [k1-2], ANS [k1-1], a [I]) <= 0) 39 {40 K1 --; 41} 42 ans [K1 ++] = A [I]; 43} 44 int k2 = k1; 45 for (INT I = s-1; I> = 0; I --) // top convex hull, scanning points from above; 46 {47 While (K1> k2 & judge (ANS [k1-2], ANS [k1-1], a [I]) <= 0) 48 {49 K1 --; 50} 51 ans [K1 ++] = A [I]; 52} 53 K1 --; 54 sort (ANS, ANS + k1); 55 for (INT I = 0; I <K1; I ++) 56 printf ("% d \ n", ANS [I]. x, ANS [I]. y); 57} 58 return 0; 59}

 

Nyoj 78 ring pool (Entry level convex hull)