HDU 1392 HDU 1348 凸包

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求凸包的周长，注意n=1 ， 2时特殊情况

int  cmp(double x){     if(fabs(x) < 1e-8) return 0 ;     if(x > 0) return 1 ;     return -1  ;}struct point{       double  x ,  y  ;       point(){}       point(double _x , double _y):x(_x) , y(_y){}       friend bool operator == (const point &a , const point &b){              return cmp(a.x - b.x) == 0 && cmp(a.y - b.y) == 0 ;       }       friend double operator ^ (const point &a , const point &b){              return a.x * b.y - a.y * b.x ;       }       friend double dist(const  point &a , const point &b){              return  sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) ) ;       }       point operator - (point o){             return  point(x - o.x , y - o.y) ;       }};bool  cmpless(const  point &a , const point &b){      return   cmp(a.x - b.x) < 0            || cmp(a.x - b.x == 0) && cmp(a.y - b.y) < 0 ;}vector<point> convex_hull(vector<point> a){     vector<point> src(2 * a.size() + 5)  ;     sort(a.begin() , a.end() , cmpless) ;     a.erase(unique(a.begin() , a.end()) , a.end())  ;     int m = 0 ;     for(int i = 0 ; i < a.size() ; i++){          while(m > 1 && cmp( (src[m-1] - src[m-2]) ^  (a[i] - src[m-2]) ) <= 0)              m-- ;          src[m++] = a[i] ;     }     int k = m ;     for(int i = a.size() - 2 ; i >= 0 ; i--){          while(m > k && cmp( (src[m-1] - src[m-2]) ^ (a[i] - src[m-2])) <= 0)              m-- ;          src[m++] = a[i] ;     }     src.resize(m) ;     if(a.size() > 1) src.resize(m-1) ;     return src ;}int   main(){      int n  ,  i   ;      double  ans ;      while(cin>>n && n){           vector<point> lis(n) ;           for(i = 0 ; i < n ; i++)                scanf("%lf%lf" , &lis[i].x , &lis[i].y) ;           if(n == 1) ans = 0.0  ;           else if(n == 2) ans =  dist(lis[0] , lis[1]) ;           else{                vector<point> a = convex_hull(lis) ;                ans = 0.0 ;                for(i = 0 ; i < a.size() ; i++)                      ans += dist(a[i] , a[(i+1) % a.size()])  ;           }           printf("%.2lf\n" , ans) ;      }      return  0  ;}

hdu 1348

int  cmp(double x){     if(fabs(x) < 1e-8) return 0 ;     if(x > 0) return 1 ;     return -1  ;}struct point{       double  x ,  y  ;       point(){}       point(double _x , double _y):x(_x) , y(_y){}       friend bool operator == (const point &a , const point &b){              return cmp(a.x - b.x) == 0 && cmp(a.y - b.y) == 0 ;       }       friend double operator ^ (const point &a , const point &b){              return a.x * b.y - a.y * b.x ;       }       friend double dist(const  point &a , const point &b){              return  sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) ) ;       }       point operator - (point o){             return  point(x - o.x , y - o.y) ;       }};bool  cmpless(const  point &a , const point &b){      return   cmp(a.x - b.x) < 0            || cmp(a.x - b.x == 0) && cmp(a.y - b.y) < 0 ;}vector<point> convex_hull(vector<point> a){     vector<point> src(2 * a.size() + 5)  ;     sort(a.begin() , a.end() , cmpless) ;     a.erase(unique(a.begin() , a.end()) , a.end())  ;     int m = 0 ;     for(int i = 0 ; i < a.size() ; i++){          while(m > 1 && cmp( (src[m-1] - src[m-2]) ^  (a[i] - src[m-2]) ) <= 0)              m-- ;          src[m++] = a[i] ;     }     int k = m ;     for(int i = a.size() - 2 ; i >= 0 ; i--){          while(m > k && cmp( (src[m-1] - src[m-2]) ^ (a[i] - src[m-2])) <= 0)              m-- ;          src[m++] = a[i] ;     }     src.resize(m) ;     if(a.size() > 1) src.resize(m-1) ;     return src ;}int   main(){      int n  ,  i  , t  , T = 1  ;      double  ans  , r ;      cin>>t  ;      while(t--){           cin>>n>>r ;           vector<point> lis(n) ;           for(i = 0 ; i < n ; i++)                scanf("%lf%lf" , &lis[i].x , &lis[i].y) ;           if(n == 1) ans = 0.0  ;           else if(n == 2) ans =  dist(lis[0] , lis[1]) ;           else{                vector<point> a = convex_hull(lis) ;                ans = 0.0 ;                for(i = 0 ; i < a.size() ; i++)                      ans += dist(a[i] , a[(i+1) % a.size()])  ;           }           if(T++ != 1) puts("") ;           printf("%.0lf\n" , ans + 2.0 * acos(-1.0) * r) ;      }      return  0  ;}

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