题目大意

题目链接

给出正n边形n个点的坐标， 求n变形面积的2倍， 3<=N<=100000，0<=xi,yi<=10^9， mod = 1000000007

AC代码

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#include <bits/stdc++.h>
#define eps 1e-8
using namespace std;
#define ms(a, b) memset((a), (b), sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
const int N = 1e5 + 5;
const int INF = 0x3f3f3f3f;
const ll ll_max = 4557430888798830399;
const int mod = 1e9 + 7;
inline ll read() {
    ll res = 0; bool f = 0; char ch = getchar();
    while (ch < '0' || ch > '9') { if (ch == '-') f = 1; ch = getchar(); }
    while (ch <= '9' && ch >= '0') { res = (res << 3) + (res << 1) + ch - '0'; ch = getchar(); }
    return f ? (~ res  + 1) : res;
}

struct node{
    ll x, y;
}a[N];
int n;
ll ans;
int main(){
    while(~scanf("%d", &n)){
        for (int i = 0; i < n; ++i) a[i].x = read(), a[i].y = read();
        a[n] = a[0];
        ans = 0;
        for (int i = 1; i <= n; ++i)
            ans = (ans + (a[i - 1].x * a[i].y - a[i].x * a[i - 1].y) % mod + mod) % mod;
        printf("%lld\n", ans);
    }

    return 0;
}
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恰似你一低头的温柔，娇弱水莲花不胜寒风的娇羞， 我的心为你悸动不休。  --mingfuyan