【HDOJ】5128

暴力+计算几何。

 /* 5128 */
 #include <iostream>
 #include <algorithm>
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 using namespace std;

 typedef struct point {
     int x, y;
     point() {}
     point(int xx, int yy) {
         x = xx; y = yy;
     }
     friend bool operator <(const point &a, const point &b) {
         if (a.x == b.x)
             return a.y < b.y;
         else
             return a.x < b.x;
     }
 } point;

 typedef struct {
     point v[];
 } square_t ;

 #define MAXN 35

 int n, m;
 point p[MAXN];
 point sq[];
 square_t q[];

 bool isSquare() {
     if (sq[].x!=sq[].x || sq[].y!=sq[].y || sq[].y!=sq[].y || sq[].x!=sq[].x)
         return false;
     return sq[].x!=sq[].x && sq[].y!=sq[].y;
 }

 bool isTouch(int i, int j) {
     for (int u=; u<; ++u) {
         for (int v=; v<; ++v) {
             if (q[i].v[u].x==q[j].v[v].x && q[i].v[u].y==q[j].v[v].y)
                 return true;
         }
     }
     if ((q[i].v[].x==q[j].v[].x || q[i].v[].x==q[j].v[].x || q[i].v[].x==q[j].v[].x || q[i].v[].x==q[j].v[].x) && !(q[j].v[].y>q[i].v[].y || q[i].v[].y>q[j].v[].y))
         return true;
     if ((q[i].v[].y==q[j].v[].y || q[i].v[].y==q[j].v[].y || q[i].v[].y==q[j].v[].y || q[i].v[].y==q[j].v[].y) && !(q[j].v[].x>q[i].v[].x || q[i].v[].x>q[j].v[].x))
         return true;
     return false;
 }

 bool isCross(int i, int j) {
     return q[i].v[].x<=q[j].v[].x && q[i].v[].y<=q[j].v[].y && q[i].v[].x>=q[j].v[].x && q[i].v[].x>=q[j].v[].y && q[i].v[].x<=q[j].v[].x && q[i].v[].y<=q[j].v[].y;
 }

 bool isIncluded(int i, int j) {
     return q[i].v[].x<q[j].v[].x && q[i].v[].y<q[j].v[].y && q[i].v[].x>q[j].v[].x && q[i].v[].y>q[j].v[].y;
 }

 int main() {
     int i, j, k, r;
     int ans;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     while (scanf("%d",&n)!=EOF && n) {
         for (i=; i<n; ++i)
             scanf("%d %d", &p[i].x, &p[i].y);
         if (n < ) {
             puts("imp");
             continue;
         }
         sort(p, p+n);
         m = ;
         for (i=; i<n; ++i) {
             for (j=; j<n; ++j) {
                 if (i == j)
                     continue;
                 for (k=; k<n; ++k) {
                     if (k==i || k==j)
                         continue;
                     for (r=; r<n; ++r) {
                         if (r==i || r==j || r==k)
                             continue;
                         sq[] = p[i];
                         sq[] = p[j];
                         sq[] = p[k];
                         sq[] = p[r];
                         sort(sq, sq+);
                         if (isSquare()) {
                             q[m].v[] = sq[];
                             q[m].v[] = sq[];
                             q[m].v[] = sq[];
                             q[m].v[] = sq[];
                             ++m;
                         }
                     }
                 }
             }
         }
         ans = -;
         for (i=; i<m; ++i) {
             for (j=; j<m; ++j) {
                 if (i == j)
                     continue;
                 if (isTouch(i, j) || isCross(j, i) || isCross(i, j))
                     continue;
                 if (isIncluded(i, j)) {
                     k = (q[i].v[].x - q[i].v[].x) * (q[i].v[].y - q[i].v[].y);
                 } else if (isIncluded(j, i)) {
                     k = (q[j].v[].x - q[j].v[].x) * (q[j].v[].y - q[j].v[].y);
                 } else {
                     k = (q[i].v[].x - q[i].v[].x) * (q[i].v[].y - q[i].v[].y) +\
                         (q[j].v[].x - q[j].v[].x) * (q[j].v[].y - q[j].v[].y);
                 }
                 if (k > ans)
                     ans = k;
             }
         }
         if (ans < )
             puts("imp");
         else
             printf("%d\n", ans);
     }

     return ;
 }