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#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define int long long
struct p{
	int x, y;
};
struct vec{
	int x, y;
	vec(const p& a, const p& b){
		x = b.x - a.x;
		y = b.y - a.y;
	}
 
};
 
ll dot(vec a, vec b){
	return a.x * b.x + a.y * b.y;
}
 
ll cross(vec a, vec b){
	return 1LL * a.x * b.y - 1LL * b.x * a.y;
}
 
const double eps = 1e-9;
 
int sign(int x){
	if(x > eps) return 1;
	if(x < -eps) return -1;
	return 0;
}
 
signed main() {
	int n;cin >> n;
	p a[n];
	for(int i = 0; i < n; i++){
		cin >> a[i].x >> a[i].y;
	}
	ll s = 0;
	for(int i = 1; i < n - 1; i++){
		s += cross(vec(a[0], a[i]), vec(a[0], a[i + 1]));
		cout << cross(vec(a[0], a[i]), vec(a[0], a[i + 1])) << endl;
	}
	cout << s;
}

Success #stdin #stdout 0.01s 5320KB

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https://ideone.com/JUdqb0

language:

C++14 (gcc 8.3)

created:

visibility:

public

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