[Codevs 1249] Polygon Area, codevs1249 Area

[Codevs 1249] Polygon Area, codevs1249 Area

Question:

The Cross product is used to represent the directed area. You can also calculate the area of the concave polygon.

Code:

Total time consumption: 5 ms
Total memory consumption: 256 kB

#include<cstdio>#include<cmath>#include<vector>#include<algorithm>using namespace std;const int maxn = 100 + 10;int n;struct Point {    int x, y;    Point(int x=0, int y=0):x(x),y(y) {}}P[maxn];typedef Point Vector;Vector operator + (Vector A, Vector B) { return Vector(A.x+B.x, A.y+B.y); }Vector operator - (Vector A, Vector B) { return Vector(A.x-B.x, A.y-B.y); }Vector operator * (Vector A, int p) { return Vector(A.x*p, A.y*p); }Vector operator / (Vector A, int p) { return Vector(A.x/p, A.y/p); }bool operator < (const Vector& a, const Vector& b) {    return a.x < b.x || (a.x == b.x && a.y < b.y);}int Dot(Vector A, Vector B) { return A.x*B.x + A.y*B.y; }int Length(Vector A) { return sqrt(Dot(A, A)); }int Angle(Vector A, Vector B) { return acos(Dot(A, B) / Length(A) / Length(B)); }int Cross(Vector A, Vector B) { return A.x*B.y - A.y*B.x; }int Area2(Point A, Point B, Point C) { return Cross(B-A, C-A); }int PolygonArea() {    int area = 0;    for(int i = 1; i < n-1; i++)         area += Cross(P[i]-P[0], P[i+1]-P[0]);    return area/2;}int main() {    scanf("%d", &n);    for(int i = 0; i < n; i++)         scanf("%d%d", &P[i].x, &P[i].y);    printf("%d\n", PolygonArea());    return 0;}