题目链接：https://vjudge.net/problem/POJ-1113
题目链接：https://vjudge.net/problem/POJ-3348
安德鲁真的巨快无比。
具体看注释
1 /************************************************************************* 2 > File Name: poj2079.cpp 3 # File Name: poj2079.cpp 4 # Author : xiaobuxie 5 # QQ : 760427180 6 # Email:[email protected] 7 # Created Time: 2019年10月12日 星期六 17时55分28秒 8 ************************************************************************/ 9 10 #include<iostream> 11 #include<cstdio> 12 #include<map> 13 #include<cmath> 14 #include<cstring> 15 #include<set> 16 #include<queue> 17 #include<vector> 18 #include<algorithm> 19 using namespace std; 20 typedef long long ll; 21 #define inf 0x3f3f3f3f 22 #define pq priority_queue<int,vector<int>,greater<int> > 23 ll gcd(ll a,ll b){ 24 if(a<b) return gcd(b,a); 25 return b==0?a:gcd(b,a%b); 26 } 27 28 const double pi = acos(-1.0); 29 const int N = 5e4+9; 30 struct Point{ 31 double x,y; 32 bool operator < (const Point& b)const{ 33 return x<b.x || (x==b.x && y<b.y); 34 } 35 Point operator - (const Point& b)const{ 36 return (Point){x-b.x,y-b.y}; 37 } 38 double operator ^ (const Point& b)const{ 39 return x*b.y - b.x*y; 40 } 41 }p[N],ch[N]; 42 int n; 43 inline void init(){ 44 for(int i =0 ;i<n;++i) scanf("%lf %lf",&p[i].x,&p[i].y); 45 } 46 double dis(Point a,Point b){ 47 return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) ); 48 } 49 50 /* 51 m代表着top,凸包是从0到m-1 52 一开始求下凸包，接下来求上凸包 53 求出来的凸包是逆时针的 54 */ 55 inline int Andrew(){ 56 sort(p,p+n); 57 int m = 0; 58 for(int i = 0; i < n;++i){ 59 while( m>1 && ((p[i] - ch[m-2]) ^ (ch[m-1] - ch[m-2])) >=0) --m; 60 ch[m++] = p[i]; 61 } 62 int k = m; 63 for(int i = n-2;i >= 0;--i){ 64 while( m>k && ((p[i] - ch[m-2]) ^ (ch[m-1] - ch[m-2])) >=0) --m; 65 ch[m++] = p[i]; 66 } 67 if(n>1) --m; 68 return m; 69 } 70 int main(){ 71 while(~scanf("%d",&n)){ 72 int L; 73 scanf("%d",&L); 74 init(); 75 int m = Andrew(); 76 ch[m] = ch[0]; 77 double ans = 0; 78 for(int i = 0;i < m;++i) ans += dis(ch[i],ch[i+1]); 79 ans += 2*pi*L; 80 printf("%d\n",(int)(ans+0.5)); 81 } 82 return 0; 83 }
1 /************************************************************************* 2 > File Name: poj2079.cpp 3 # File Name: poj2079.cpp 4 # Author : xiaobuxie 5 # QQ : 760427180 6 # Email:[email protected] 7 # Created Time: 2019年10月12日 星期六 17时55分28秒 8 ************************************************************************/ 9 10 #include<iostream> 11 #include<cstdio> 12 #include<map> 13 #include<cmath> 14 #include<cstring> 15 #include<set> 16 #include<queue> 17 #include<vector> 18 #include<algorithm> 19 using namespace std; 20 typedef long long ll; 21 #define inf 0x3f3f3f3f 22 #define pq priority_queue<int,vector<int>,greater<int> > 23 ll gcd(ll a,ll b){ 24 if(a<b) return gcd(b,a); 25 return b==0?a:gcd(b,a%b); 26 } 27 28 const double pi = acos(-1.0); 29 const int N = 5e4+9; 30 struct Point{ 31 double x,y; 32 bool operator < (const Point& b)const{ 33 return x<b.x || (x==b.x && y<b.y); 34 } 35 Point operator - (const Point& b)const{ 36 return (Point){x-b.x,y-b.y}; 37 } 38 double operator ^ (const Point& b)const{ 39 return x*b.y - b.x*y; 40 } 41 }p[N],ch[N]; 42 int n; 43 inline void init(){ 44 for(int i =0 ;i<n;++i) scanf("%lf %lf",&p[i].x,&p[i].y); 45 } 46 /* 47 m代表着top,凸包是从0到m-1 48 一开始求下凸包，接下来求上凸包 49 求出来的凸包是逆时针的 50 */ 51 inline int Andrew(){ 52 sort(p,p+n); 53 int m = 0; 54 for(int i = 0; i < n;++i){ 55 while( m>1 && ((p[i] - ch[m-2]) ^ (ch[m-1] - ch[m-2])) >=0) --m; 56 ch[m++] = p[i]; 57 } 58 int k = m; 59 for(int i = n-2;i >= 0;--i){ 60 while( m>k && ((p[i] - ch[m-2]) ^ (ch[m-1] - ch[m-2])) >=0) --m; 61 ch[m++] = p[i]; 62 } 63 if(n>1) --m; 64 return m; 65 } 66 int main(){ 67 while(~scanf("%d",&n)){ 68 init(); 69 if(n<3){ 70 puts("0"); 71 continue; 72 } 73 int m = Andrew(); 74 double ans = 0; 75 for(int i = 1;i < m-1;++i) ans += ((ch[i]-ch[0]) ^ (ch[i+1]-ch[0])); 76 ans /= 2; 77 printf("%d\n",(int)(ans/50.0)); 78 } 79 return 0; 80 }