Kattis - convexpolygonarea 【数学】

题意

给出一系列点，求这个多边形面积

思路

向量叉积

AC代码

#include <cstdio>

#include <cstring>

#include <ctype.h>

#include <cstdlib>

#include <iostream>

#include <algorithm>

#include <cmath>

#include <deque>

#include <vector>

#include <queue>

#include <string>

#include <map>

#include <stack>

#include <set>

#include <numeric>

#include <sstream>

using namespace std;

typedef long long LL;

const double PI  = 3.14159265358979323846264338327;

const double E   = 2.718281828459;

const double eps = 1e-6;

const int MAXN = 0x3f3f3f3f;

const int MINN = 0xc0c0c0c0;

const int maxn = 1e2 + 5;

const int MOD  = 1e9 + 7;

struct Node

{

    double x;

    double y;

}G[maxn];

double Cross(Node a, Node b)

{

    return a.x * b.y - a.y * b.x;

}

int main()

{

    int t;

    cin >> t;

    while (t--)

    {

        int n;

        cin >> n;

        for (int i = 0; i < n; i++)

            scanf("%lf%lf", &G[i].x, &G[i].y);

        double sum = 0;

        G[n].x = G[0].x;

        G[n].y = G[0].y;

        for (int i = 0; i < n; i++)

            sum += Cross(G[i], G[i + 1]);

        sum = sum / 2.0;

        cout << sum << endl;

    }

}

巴特西

Kattis - convexpolygonarea 【数学】

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