ADDED   SRM/634-U/1A.cpp
Index: SRM/634-U/1A.cpp
==================================================================
--- SRM/634-U/1A.cpp
+++ SRM/634-U/1A.cpp
@@ -0,0 +1,124 @@
+#include <iostream>
+#include <sstream>
+#include <iomanip>
+#include <vector>
+#include <string>
+#include <map>
+#include <set>
+#include <algorithm>
+#include <numeric>
+#include <iterator>
+#include <functional>
+#include <complex>
+#include <queue>
+#include <stack>
+#include <cmath>
+#include <cassert>
+#include <tuple>
+using namespace std;
+typedef long long LL;
+typedef complex<double> CMP;
+
+class ShoppingSurveyDiv1 { public:
+	int minValue(int N, int K, vector <int> s)
+	{
+		for(int big=0; big<=N; ++big)
+			if(can(N, K, s, big))
+				return big;
+
+		assert(false);
+		return -1;
+	}
+
+	bool can(int N, int K, vector<int> sb, int BIG)
+	{
+		sort(sb.rbegin(), sb.rend());
+		assert(sb[K-1] >= BIG);
+
+		multiset<int, greater<int>> s;
+		for(auto p: sb)
+			if(p-BIG > 0)
+				s.insert(p-BIG);
+		int total = accumulate(s.begin(), s.end(), 0);
+		if(total > (K-1)*(N-BIG))
+			return false;
+		if(!s.empty() && *s.begin() > (N-BIG))
+			return false;
+		return true;
+	}
+};
+
+// BEGIN CUT HERE
+#include <ctime>
+double start_time; string timer()
+ { ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
+template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
+ { os << "{ ";
+   for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
+   os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
+void verify_case(const int& Expected, const int& Received) {
+ bool ok = (Expected == Received);
+ if(ok) cerr << "PASSED" << timer() << endl;  else { cerr << "FAILED" << timer() << endl;
+ cerr << "\to: \"" << Expected << '\"' << endl << "\tx: \"" << Received << '\"' << endl; } }
+#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
+#define END	 verify_case(_, ShoppingSurveyDiv1().minValue(N, K, s));}
+int main(){
+
+CASE(0)
+	int N = 10; 
+	int K = 2; 
+	int s_[] = {1, 2, 3};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = 0; 
+END
+CASE(1)
+	int N = 5; 
+	int K = 2; 
+	int s_[] = {1, 2, 3};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = 1; 
+END
+CASE(2)
+	int N = 4; 
+	int K = 4; 
+	int s_[] = {4, 4, 4, 2};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = 2; 
+END
+CASE(3)
+	int N = 20; 
+	int K = 3; 
+	int s_[] = {1, 10, 3, 4, 8, 15, 3, 16, 18, 2, 7, 3};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = 10; 
+END
+CASE(4)
+	int N = 4; 
+	int K = 2; 
+	int s_[] = {1, 2, 1, 1, 3, 1, 2, 2, 1, 2, 1};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = 2; 
+END
+CASE(5)
+	int N = 2; 
+	int K = 3; 
+	int s_[] = {1, 1, 1, 2};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = 1; 
+END
+CASE(6)
+	int N = 500; 
+	int K = 1; 
+	int s_[] = {500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = -1; 
+END
+CASE(6)
+	int N = 500; 
+	int K = 500; 
+	int s_[] = {500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500,500};
+	  vector <int> s(s_, s_+sizeof(s_)/sizeof(*s_)); 
+	int _ = -1; 
+END
+}
+// END CUT HERE

ADDED   SRM/634-U/1B.cpp
Index: SRM/634-U/1B.cpp
==================================================================
--- SRM/634-U/1B.cpp
+++ SRM/634-U/1B.cpp
@@ -0,0 +1,311 @@
+#include <iostream>
+#include <sstream>
+#include <iomanip>
+#include <vector>
+#include <string>
+#include <map>
+#include <set>
+#include <algorithm>
+#include <numeric>
+#include <iterator>
+#include <functional>
+#include <complex>
+#include <queue>
+#include <stack>
+#include <cmath>
+#include <cassert>
+#include <tuple>
+using namespace std;
+typedef long long LL;
+
+template<typename T>
+class IdGen
+{
+	map<T, int> v2id_;
+	vector<T>   id2v_;
+public:
+	int v2id(const T& v) {
+		if( !v2id_.count(v) ) { v2id_[v] = size(); id2v_.push_back(v); }
+		return v2id_[v];
+	}
+	const T& id2v(int i) const { return id2v_[i]; }
+	int size() const { return id2v_.size(); }
+};
+
+template<typename Vert, typename Flow, int NV=2048>
+class MaxFlow
+{
+	IdGen<Vert> idgen;
+	vector<int> G[NV];
+	Flow F[NV][NV];
+
+public:
+	void addEdge( Vert s_, Vert t_, Flow f )
+	{
+		const int s = idgen.v2id(s_), t = idgen.v2id(t_);
+		G[s].push_back(t);
+		G[t].push_back(s);
+		F[s][t] = f;
+		F[t][s] = 0;
+	}
+
+	Flow calc( Vert s_, Vert t_ )
+	{
+		const int S = idgen.v2id(s_), D = idgen.v2id(t_);
+		for( Flow total=0 ;; ) {
+			// Do BFS and compute the level for each node.
+			int LV[NV] = {0};
+			vector<int> Q(1, S);
+			for(int lv=1; !Q.empty(); ++lv) {
+				vector<int> Q2;
+				for(size_t i=0; i!=Q.size(); ++i) {
+					const vector<int>& ne = G[Q[i]];
+					for(size_t j=0; j!=ne.size(); ++j)
+						if( F[Q[i]][ne[j]] && !LV[ne[j]] && ne[j]!=S )
+							LV[ne[j]]=lv, Q2.push_back(ne[j]);
+				}
+				Q.swap(Q2);
+			}
+
+			// Destination is now unreachable. Done.
+			if( !LV[D] )
+				return total;
+
+			// Iterating DFS.
+			bool blocked[NV] = {};
+			total += dinic_dfs( S, D, LV, 0x7fffffff, blocked );
+		}
+	}
+
+private:
+	Flow dinic_dfs( int v, int D, int LV[], Flow flow_in, bool blocked[] )
+	{
+		Flow flow_out = 0;
+		for(size_t i=0; i!=G[v].size(); ++i) {
+			int u = G[v][i];
+			if( LV[v]+1==LV[u] && F[v][u] ) {
+				Flow f = min(flow_in-flow_out, F[v][u]);
+				if( u==D || !blocked[u] && (f=dinic_dfs(u,D,LV,f,blocked))>0 ) {
+					F[v][u]  -= f;
+					F[u][v]  += f;
+					flow_out += f;
+					if( flow_in == flow_out ) return flow_out;
+				}
+			}
+		}
+		blocked[v] = (flow_out==0);
+		return flow_out;
+	}
+};
+
+
+typedef complex<int> CMP;
+double outer_prod(const CMP& a, const CMP& b) { return imag(conj(a)*b); }
+double inner_prod(const CMP& a, const CMP& b) { return real(conj(a)*b); }
+int ccw(const CMP& a, CMP b, CMP c) {
+	b -= a; c -= a;
+	if( outer_prod(b,c) > 0 ) return +1; // counter clockwise
+	if( outer_prod(b,c) < 0 ) return -1; // clockwise
+	if( inner_prod(b,c) < 0 ) return +2; // c--[a--b] on line
+	if( norm(b) < norm(c) )   return -2; // [a--b]--c on line
+	return 0; // [a--c--b] on line
+}
+
+bool cross(int x1, int y1, int x2, int y2,
+           int X1, int Y1, int X2, int Y2) {
+	CMP p1(x1,y1);
+	CMP p2(x2,y2);
+	CMP P1(X1,Y1);
+	CMP P2(X2,Y2);
+	return ccw(p1,p2,P1)*ccw(p1,p2,P2)<=0 && ccw(P1,P2,p1)*ccw(P1,P2,p2)<=0;
+}
+
+class SegmentDrawing { public:
+	enum TAG {SRC, LEFT_R, RIGHT_R, LEFT_B, RIGHT_B, DST};
+	static const int INF = 0x3fffffff;
+
+	int maxScore(vector <int> x, vector <int> y, vector <int> redScore, vector <int> blueScore)
+	{
+		const int N = x.size();
+
+		vector<vector<bool>> cross_table(N*N, vector<bool>(N*N));
+		for(int i=0; i<N; ++i)
+		for(int k=i+1; k<N; ++k)
+		for(int ii=0; ii<N; ++ii)
+		for(int kk=ii+1; kk<N; ++kk)
+			cross_table[i*N+k][ii*N+kk] = cross(x[i],y[i],x[k],y[k],x[ii],y[ii],x[kk],y[kk]);
+
+		auto* mf = new MaxFlow<pair<TAG,int>, LL>;
+
+		int all = 0;
+		for(int i=0; i<N; ++i)
+		for(int k=i+1; k<N; ++k) {
+			int p = i*N + k;
+			mf->addEdge(make_pair(SRC,0), make_pair(LEFT_R,p), redScore[p]);
+			mf->addEdge(make_pair(LEFT_R,p), make_pair(RIGHT_R,p), INF);
+			mf->addEdge(make_pair(RIGHT_R,p), make_pair(DST,0), 0);
+			mf->addEdge(make_pair(SRC,0), make_pair(LEFT_B,p), 0);
+			mf->addEdge(make_pair(LEFT_B,p), make_pair(RIGHT_B,p), INF);
+			mf->addEdge(make_pair(RIGHT_B,p), make_pair(DST,0), blueScore[p]);
+			all += redScore[p];
+			all += blueScore[p];
+		}
+
+		for(int i=0; i<N; ++i)
+		for(int k=i+1; k<N; ++k)
+		for(int ii=0; ii<N; ++ii)
+		for(int kk=ii+1; kk<N; ++kk) {
+			int rp = i*N + k;
+			int bp = ii*N + kk;
+			if(cross_table[rp][bp])
+				mf->addEdge(make_pair(RIGHT_R,rp), make_pair(LEFT_B,bp), INF);
+		}
+
+		LL flow = mf->calc(make_pair(SRC,0), make_pair(DST,0));
+		delete mf;
+		return all - flow;
+	}
+};
+
+// BEGIN CUT HERE
+#include <ctime>
+double start_time; string timer()
+ { ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
+template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
+ { os << "{ ";
+   for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
+   os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
+void verify_case(const int& Expected, const int& Received) {
+ bool ok = (Expected == Received);
+ if(ok) cerr << "PASSED" << timer() << endl;  else { cerr << "FAILED" << timer() << endl;
+ cerr << "\to: \"" << Expected << '\"' << endl << "\tx: \"" << Received << '\"' << endl; } }
+#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
+#define END	 verify_case(_, SegmentDrawing().maxScore(x, y, redScore, blueScore));}
+int main(){
+
+CASE(0)
+	int x_[] = {0,1,0,-1};
+	  vector <int> x(x_, x_+sizeof(x_)/sizeof(*x_)); 
+	int y_[] = {1,0,-1,0};
+	  vector <int> y(y_, y_+sizeof(y_)/sizeof(*y_)); 
+	int redScore_[] = {0, 1, 2, 3,
+ 1, 0, 6, 4,
+ 2, 6, 0, 5,
+ 3, 4, 5, 0};
+	  vector <int> redScore(redScore_, redScore_+sizeof(redScore_)/sizeof(*redScore_)); 
+	int blueScore_[] = {0, 2, 3, 7,
+ 2, 0, 4, 6,
+ 3, 4, 0, 5,
+ 7, 6, 5, 0};
+	  vector <int> blueScore(blueScore_, blueScore_+sizeof(blueScore_)/sizeof(*blueScore_)); 
+	int _ = 27; 
+END
+CASE(1)
+	int x_[] = {0, 1};
+	  vector <int> x(x_, x_+sizeof(x_)/sizeof(*x_)); 
+	int y_[] = {1, 0};
+	  vector <int> y(y_, y_+sizeof(y_)/sizeof(*y_)); 
+	int redScore_[] = {0, 101, 101, 0};
+	  vector <int> redScore(redScore_, redScore_+sizeof(redScore_)/sizeof(*redScore_)); 
+	int blueScore_[] = {0, 100, 100, 0};
+	  vector <int> blueScore(blueScore_, blueScore_+sizeof(blueScore_)/sizeof(*blueScore_)); 
+	int _ = 101; 
+END
+CASE(2)
+	int x_[] = {-3, -1, -1,  1,  1,  3};
+	  vector <int> x(x_, x_+sizeof(x_)/sizeof(*x_)); 
+	int y_[] = { 0, -2,  2, -2,  2,  0};
+	  vector <int> y(y_, y_+sizeof(y_)/sizeof(*y_)); 
+	int redScore_[] = {0, 2, 1, 2, 1, 2,
+ 2, 0, 2, 1, 2, 1,
+ 1, 2, 0, 2, 1, 2,
+ 2, 1, 2, 0, 2, 1,
+ 1, 2, 1, 2, 0, 2,
+ 2, 1, 2, 1, 2, 0};
+	  vector <int> redScore(redScore_, redScore_+sizeof(redScore_)/sizeof(*redScore_)); 
+	int blueScore_[] = {0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 21, 0, 0,
+ 0, 0, 21, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0};
+	  vector <int> blueScore(blueScore_, blueScore_+sizeof(blueScore_)/sizeof(*blueScore_)); 
+	int _ = 25; 
+END
+CASE(3)
+	int x_[] = {-100, 100, 0, -10, 10, 0};
+	  vector <int> x(x_, x_+sizeof(x_)/sizeof(*x_)); 
+	int y_[] = {0, 0, 100, 10, 10, 1};
+	  vector <int> y(y_, y_+sizeof(y_)/sizeof(*y_)); 
+	int redScore_[] = { 0, 96, 96, 25, 25, 25,
+ 96,  0, 96, 25, 25, 25,
+ 96, 96,  0, 25, 25, 25,
+ 25, 25, 25,  0, 10, 10,
+ 25, 25, 25, 10,  0, 10,
+ 25, 25, 25, 10, 10,  0};
+	  vector <int> redScore(redScore_, redScore_+sizeof(redScore_)/sizeof(*redScore_)); 
+	int blueScore_[] = { 0, 30, 30, 20, 20, 20,
+ 30,  0, 30, 20, 20, 20,
+ 30, 30,  0, 20, 20, 20,
+ 20, 20, 20,  0, 86, 86,
+ 20, 20, 20, 86,  0, 86,
+ 20, 20, 20, 86, 86,  0};
+	  vector <int> blueScore(blueScore_, blueScore_+sizeof(blueScore_)/sizeof(*blueScore_)); 
+	int _ = 546; 
+END
+CASE(4)
+	int x_[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+	  vector <int> x(x_, x_+sizeof(x_)/sizeof(*x_)); 
+	int y_[] = {1, 4, 9, 16, 25, 36, 49, 64, 81, 100};
+	  vector <int> y(y_, y_+sizeof(y_)/sizeof(*y_)); 
+	int redScore_[] = {0, 15, 2, 3, 4, 5, 6, 7, 8, 9,
+ 15, 0, 15, 2, 3, 4, 5, 6, 7, 8,
+ 2, 15, 0, 15, 2, 3, 4, 5, 6, 7,
+ 3, 2, 15, 0, 15, 2, 3, 4, 5, 6,
+ 4, 3, 2, 15, 0, 15, 2, 3, 4, 5,
+ 5, 4, 3, 2, 15, 0, 15, 2, 3, 4,
+ 6, 5, 4, 3, 2, 15, 0, 15, 2, 3,
+ 7, 6, 5, 4, 3, 2, 15, 0, 15, 2,
+ 8, 7, 6, 5, 4, 3, 2, 15, 0, 15,
+ 9, 8, 7, 6, 5, 4, 3, 2, 15, 0}
+;
+	  vector <int> redScore(redScore_, redScore_+sizeof(redScore_)/sizeof(*redScore_)); 
+	int blueScore_[] = {0, 0, 2, 3, 4, 5, 6, 7, 8, 9,
+ 0, 0, 0, 2, 3, 4, 5, 6, 7, 8,
+ 2, 0, 0, 0, 2, 3, 4, 5, 6, 7,
+ 3, 2, 0, 0, 0, 2, 3, 4, 5, 6,
+ 4, 3, 2, 0, 0, 100, 2, 3, 4, 5,
+ 5, 4, 3, 2, 100, 0, 0, 2, 3, 4,
+ 6, 5, 4, 3, 2, 0, 0, 0, 2, 3,
+ 7, 6, 5, 4, 3, 2, 0, 0, 0, 2,
+ 8, 7, 6, 5, 4, 3, 2, 0, 0, 0,
+ 9, 8, 7, 6, 5, 4, 3, 2, 0, 0};
+	  vector <int> blueScore(blueScore_, blueScore_+sizeof(blueScore_)/sizeof(*blueScore_)); 
+	int _ = 300; 
+END
+/*
+CASE(5)
+	int x_[] = ;
+	  vector <int> x(x_, x_+sizeof(x_)/sizeof(*x_)); 
+	int y_[] = ;
+	  vector <int> y(y_, y_+sizeof(y_)/sizeof(*y_)); 
+	int redScore_[] = ;
+	  vector <int> redScore(redScore_, redScore_+sizeof(redScore_)/sizeof(*redScore_)); 
+	int blueScore_[] = ;
+	  vector <int> blueScore(blueScore_, blueScore_+sizeof(blueScore_)/sizeof(*blueScore_)); 
+	int _ = ; 
+END
+CASE(6)
+	int x_[] = ;
+	  vector <int> x(x_, x_+sizeof(x_)/sizeof(*x_)); 
+	int y_[] = ;
+	  vector <int> y(y_, y_+sizeof(y_)/sizeof(*y_)); 
+	int redScore_[] = ;
+	  vector <int> redScore(redScore_, redScore_+sizeof(redScore_)/sizeof(*redScore_)); 
+	int blueScore_[] = ;
+	  vector <int> blueScore(blueScore_, blueScore_+sizeof(blueScore_)/sizeof(*blueScore_)); 
+	int _ = ; 
+END
+*/
+}
+// END CUT HERE

Index: lib/geo/ccw.cpp
==================================================================
--- lib/geo/ccw.cpp
+++ lib/geo/ccw.cpp
@@ -14,5 +14,11 @@
 	if( outer_prod(b,c) < 0 ) return -1; // clockwise
 	if( inner_prod(b,c) < 0 ) return +2; // c--[a--b] on line
 	if( norm(b) < norm(c) )   return -2; // [a--b]--c on line
 	return 0; // [a--c--b] on line
 }
+
+
+// intersection of two line segments.
+bool cross(CMP p1, CMP p2, CMP P1, CMP P2) {
+	return ccw(p1,p2,P1)*ccw(p1,p2,P2)<=0 && ccw(P1,P2,p1)*ccw(P1,P2,p2)<=0;
+}