poj Fishnet

http://poj.org/problem?id=1408

  1 #include<cstdio>

  2 #include<cstring>

  3 #include<cmath>

  4 #include<algorithm>

  5 #define maxn 1000

  6 using namespace std;

  7 

  8 const double eps=1e-8;

  9 const double pi=acos(-1.0);

 10 

 11 int cmp(double x)

 12 {

 13     if(fabs(x)<eps) return 0;

 14     if(x>0) return 1;

 15     return -1;

 16 }

 17 

 18 struct point

 19 {

 20     double x,y;

 21     point(){}

 22     point(double a,double b):x(a),y(b) {}

 23     friend point operator -(const point &a,const point &b){

 24         return point(a.x-b.x,a.y-b.y);

 25     }

 26     friend point operator * (const point &a,const double b)

 27     {

 28         return point (a.x*b,a.y*b);

 29     }

 30     friend point operator / (const point &a,const double b)

 31     {

 32         return point(a.x/b,a.y/b);

 33     }

 34 };

 35 struct line

 36 {

 37     point a,b;

 38     line(){}

 39     line(point x,point y):a(x),b(y){}

 40 };

 41 inline double sqr(double x)

 42 {

 43     return x*x;

 44 }

 45 double det(point a,point b)

 46 {

 47     return a.x*b.y-a.y*b.x;

 48 }

 49 double dot(point a,point b)

 50 {

 51     return a.x*b.x+a.y*b.y;

 52 }

 53 double dist(point a,point b)

 54 {

 55     return sqrt(sqr(a.x-b.x)+sqr(a.y-b.y));

 56 }

 57 double area(point a[])

 58 {

 59     double sum=0;

 60     a[4]=a[0];

 61     for(int i=0; i<4; i++)

 62     {

 63         sum+=det(a[i+1],a[i]);

 64     }

 65     return sum/2;

 66 }

 67 

 68 bool parallel (line a,line b)

 69 {

 70     return !cmp(det(a.a-a.b,b.a-b.b));

 71 }

 72 

 73 bool line_make_point(line a,line b,point &res)

 74 {

 75     if(parallel(a,b)) return false;

 76     double s1=det(a.a-b.a,b.b-b.a);

 77     double s2=det(a.b-b.a,b.b-b.a);

 78     res=(a.b*s1-a.a*s2)/(s1-s2);

 79     return true;

 80 }

 81 

 82 int main()

 83 {

 84    int n;

 85    double a[maxn],b[maxn],c[maxn],d[maxn];

 86    point m[110][110];

 87    line l[110][110];

 88    while(scanf("%d",&n)&&n){

 89        double max1=eps;

 90         for(int i=1; i<=n; i++){

 91            scanf("%lf",&a[i]);

 92            m[0][i].x=a[i];

 93            m[0][i].y=0;

 94 

 95         }

 96         m[0][0].x=0;

 97         m[0][0].y=0;

 98         m[0][n+1].x=1;

 99         m[0][n+1].y=0;

100         for(int j=1; j<=n; j++){

101            scanf("%lf",&b[j]);

102            m[n+1][j].x=b[j];

103            m[n+1][j].y=1;

104         }

105         m[n+1][0].x=0;

106         m[n+1][0].y=1;

107         m[n+1][n+1].x=1;

108         m[n+1][n+1].y=1;

109         for(int k=1; k<=n; k++){

110            scanf("%lf",&c[k]);

111            m[k][0].y=c[k];

112            m[k][0].x=0;

113         }

114         for(int t=1 ; t<=n; t++){

115            scanf("%lf",&d[t]);

116            m[t][n+1].x=1;

117            m[t][n+1].y=d[t];

118         }

119         for(int i=1; i<=n; i++)

120         {

121             l[i][0].a=m[0][i];

122             l[i][0].b=m[n+1][i];

123         }

124         for(int i=1; i<=n; i++)

125         {

126             l[0][i].a=m[i][0];

127             l[0][i].b=m[i][n+1];

128         }

129         for(int i=1; i<=n; i++)

130         {

131             for(int j=1; j<=n; j++)

132             {

133                 point res;

134                 line_make_point(l[0][i],l[j][0],res);

135                 m[i][j]=res;

136             }

137         }

138         for(int i=0; i<=n+1; i++)

139         {

140             for(int j=0; j<=n+1; j++)

141             {

142                 point s[110];

143                 s[3]=m[i-1][j-1];

144                 s[2]=m[i-1][j];

145                 s[1]=m[i][j];

146                 s[0]=m[i][j-1];

147                 max1=max(max1,area(s));

148                 //printf("%.6lf ",area(s));

149             }

150             //printf("\n");

151         }

152         printf("%.6lf\n",max1);

153    }

154    return 0;

155 }

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