Create Area of Polygon.cpp

Author: nikolatechie

Area of Polygon.cpp

@@ -0,0 +1,74 @@
+#include <bits/stdc++.h>
+#include <ext/rope>
+using namespace std;
+using namespace __gnu_cxx;
+
+using ci = const int;
+using ld = long double;
+using llint = long long;
+using ullint = unsigned long long;
+using pii = pair <int,int>;
+using pcc = pair <char,char>;
+using pss = pair <string,string>;
+using vi = vector <int>;
+using vb = vector <bool>;
+using vii = vi::iterator;
+
+#define INF (1<<30)
+#define MOD 1000000007
+#define mp make_pair
+#define mt make_tuple
+#define all(c) c.begin(), c.end()
+#define ms(name,val) memset(name, val, sizeof name)
+#define np nullptr
+
+
+struct Point
+{
+    int x, y;
+};
+
+int n;
+vector <Point> v;
+
+/*
+    Polygon area is half of this matrix's discriminant
+
+    X0       Y0
+    X1       Y1
+    X2       Y2
+        ...
+    Xn-1   Yn-1
+
+    (X0*Y1 - X1*Y0)...
+*/
+
+double polygonArea()
+{
+    double area = 0;
+
+    for (int t1 = 0; t1 < n-1; ++t1)
+        area += (v[t1].x*v[t1+1].y - v[t1+1].x*v[t1].y);
+
+    area += (v[n-1].x*v[0].y - v[0].x*v[n-1].y);
+    return fabs(area) / 2.0;
+}
+
+int main()
+{
+    ios_base::sync_with_stdio(0);
+    //cin.tie(0);
+
+    cin >> n;
+    v.resize(n);
+
+    for (int t1 = 0; t1 < n; ++t1)
+        cin >> v[t1].x >> v[t1].y;
+
+    cout << polygonArea() << '\n';
+
+
+
+
+    return 0;
+}