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source/Geometry/Bulldozer.cpp

@@ -0,0 +1,60 @@
+struct ray
+{
+    ll x, y, dx, dy; int i, j;
+    ray(pll A, pll B, int i = 0, int j = 0)
+    {
+        if(A.fi == B.fi && A.se > B.se) swap(A, B), swap(i, j);
+        
+        if(A.fi>B.fi) swap(A, B), swap(i, j);
+        this->i = i; this->j = j;
+        x = A.fi; y = A.se;
+        dx = B.fi-A.fi; dy = B.se-A.se;
+    }
+    friend bool operator<(const ray& A, const ray& B)
+    {
+        return (A.dy*B.dx == B.dy*A.dx)?A.x == B.x?A.dx<B.dx:A.x<B.x:(A.dy*B.dx < B.dy*A.dx);
+    }
+};
+
+const int N = 1005;
+vector<pair<pll, int> > p; vector<ray> vec;
+int num[N];
+
+void solve()
+{
+    getint(n);
+    p.pb({{0, 0}, 0});
+    forr(i, n)
+    {
+        getll(a); getll(b); getchar(c);
+        p.pb({{a, b}, c=='R'});
+    }
+    sort(p.begin()+1, p.end());
+    forr(i, n) num[i] = i;
+        
+    Seg s(1, n, p);
+    
+    forr(i, n) fors(j, i+1, n) vec.pb(ray(p[i].fi, p[j].fi, i, j));
+    sort(all(vec));
+    
+    ll ans = s.query(1, n).m;
+    for(auto r:vec)
+    {
+        int i = r.i, j = r.j;
+        assert(num[i]+1 == num[j]);
+        
+        int ii = p[num[i]].se;
+        int jj = p[num[j]].se;
+        //printf("%d %d %d %d\n", i, j, ii, jj);
+        s.update(num[j], [ii](Dta A){return Dta(ii);});
+        //printf("%d\n", s.query(1, n).m);
+        s.update(num[i], [jj](Dta A){return Dta(jj);});
+        //printf("%d\n", s.query(1, n).m);
+        
+        swap(p[num[i]], p[num[j]]);
+        swap(num[i], num[j]);
+        
+        ans = max(ans, (ll)s.query(1, n).m);
+    }
+    printf("%lld\n", ans);
+}