codeforces 437E
题意:
题解:
#include <bits\stdc++.h>
using namespace std;
typedef long long ll;
const int mod = 1e9+7;
const int N = 201;
ll dp[N][N];
struct point{
ll x,y;
ll operator * (const point& b) const {
return x*b.y-y*b.x;
}
point operator - (const point& b) const {
point p;
p.x = x-b.x;
p.y = y-b.y;
return p;
}
}a[N];
int main() {
int n;
cin >> n;
ll s = 0;
for(int i = 1 ; i <= n ; i++){
cin >> a[i].x >> a[i].y;
s += a[i-1]*a[i];
}
s += a[n]*a[1];
if(s > 0){
for(int i = 1 ; i <= n/2 ; i++){
swap(a[i], a[n-i+1]);
}
}
for(int i = 1 ; i < n ; i++){
dp[i][i+1] = 1;
}
for(int len = 3 ; len <= n ; len++){
for(int l = 1, r = len ; r <= n ; l++, r++){
for(int k = l ; k <= r ; k++){
if((a[r]-a[l])*(a[k]-a[l]) > 0){
dp[l][r] = (dp[l][r]+dp[l][k]*dp[k][r])%mod;
}
}
}
}
cout << dp[1][n] << endl;
return 0;
}