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2.8

CodeForces - 682E

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 using namespace std;
 5 typedef long long LL;
 6
 7 // template
 8 struct Point
 9 {
10     LL x, y;
11     Point(LL x = 0, LL y = 0): x(x), y(y){}
12 };
13 typedef Point Vector;
14 Vector operator - (Vector A, Vector B){return Vector(A.x - B.x, A.y - B.y);}
15 Vector operator + (Vector A, Vector B){return Vector(A.x + B.x, A.y + B.y);}
16 bool operator < (const Point& a, const Point& b){return a.x < b.x || (a.x == b.x && a.y < b.y);}
17 LL Cross(Vector A, Vector B){return A.x * B.y - A.y * B.x;}
18
19 LL PolygonArea(Point* P, int n)
20 {
21     LL ans = 0;
22     for(int i = 1; i < n - 1; i++) ans += Cross(P[i] - P[0], P[i+1] - P[0]);
23     return ans;
24 }
25
26 int ConvexHull(Point* p, int n, Point* ch)
27 {
28     sort(p, p + n);
29     int m = 0;
30     for(int i = 0; i < n; i++)
31     {
32         while(m > 1 && Cross(ch[m-1] - ch[m-2], p[i] - ch[m-2]) <= 0) m--;
33         ch[m++] = p[i];
34     }
35     int k = m;
36     for(int i = n - 2; i >= 0; i--)
37     {
38         while(m > k && Cross(ch[m-1] - ch[m-2], p[i] - ch[m-2]) <= 0) m--;
39         ch[m++] = p[i];
40     }
41     if(n > 1) m--;
42     return m;
43 }
44
45 Point p[5555], ch[5555];
46 bool judge(int i, int j, int pos, int cnt)
47 {
48     p[0] = ch[i], p[1] = ch[j];
49     p[2] = ch[pos];
50     LL s1 = PolygonArea(p, 3);
51     p[2] = ch[(pos+1)%cnt];
52     LL s2 = PolygonArea(p, 3);
53     return s2 > s1;
54 }
55
56 int main(void)
57 {
58     int n;
59     LL S;
60     scanf("%d %I64d", &n, &S);
61     for(int i = 0; i < n; i++)
62     {
63         int a, b;
64         scanf("%d %d", &a, &b);
65         p[i].x = (LL) a, p[i].y = (LL) b;
66     }
67     int cnt = ConvexHull(p, n, ch);
68     int a, b, c, pos;
69     LL s = 0;
70     for(int i = 0; i < cnt; i++)
71     {
72         pos = (i + 2) % cnt;
73         for(int j = (i + 1) % cnt; (j + 1) % cnt != i; j = (j + 1) % cnt)
74         {
75             if(pos == j) pos = (pos + 1) % cnt;
76             while((pos + 1) % cnt != i && judge(i, j, pos, cnt)) pos = (pos + 1) % cnt;
77             p[0] = ch[i], p[1] = ch[j], p[2] = ch[pos];
78             LL tmp = PolygonArea(p, 3);
79             if(tmp > s) s = tmp, a = i, b = j, c = pos;
80         }
81     }
82     Point x = ch[a] + ch[b] - ch[c], y = ch[c] + ch[a] - ch[b], z = ch[b] + ch[c] - ch[a];
83     printf("%I64d %I64d\n", x.x, x.y);
84     printf("%I64d %I64d\n", y.x, y.y);
85     printf("%I64d %I64d\n", z.x, z.y);
86     return 0;
87 }

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