ZOJ1081 Points Within

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PS: 判断点是否在多边形内，用的绕圈法，具体参见刘汝佳的训练指南。

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <vector>#include <cmath>using namespace std;struct point {    int x, y;    point(double x=0, double y=0):x(x),y(y) {}};point operator - (point A, point B) {    return point(A.x-B.x, A.y-B.y);}double Cross(point A, point B) {    return A.x*B.y - A.y*B.x;}vector<point> v;vector<point> Contain;vector<point> check;int n, m;const double eps = 1e-10;int dcmp(double x) {    if(fabs(x)<eps) return 0;    else return x < 0 ? -1 : 1;}double Dot(point a, point b) {    return a.x*b.x + a.y*b.y;}bool OnSegment(point p, point a1, point a2) {    return dcmp(Cross(a1-p, a2-p))==0 && dcmp(Dot(a1-p, a2-p))<=0;}int isPointIn(point p) {    int wn = 0;    for(int i = 0; i < n; i++) {        if(OnSegment(p, v[i], v[(i+1)%n])) return 1;        int k = dcmp(Cross(v[(i+1)%n]-v[i], p-v[i]));        int d1 = dcmp(v[i].y-p.y);        int d2 = dcmp(v[(i+1)%n].y-p.y);        if(k>0 && d1<=0 && d2 > 0) wn++;        if(k<0 && d2<=0 && d1 > 0) wn--;    }    if(wn!=0) return 1;    else return 0;}int main(){    int T = 1;    point tmp;    bool first = false;    while(scanf("%d", &n)!=EOF && n) {        if(first) printf("\n");        else first = true;        scanf("%d", &m);        v.clear();        Contain.clear();        for(int i = 0; i < n; i++) {            scanf("%d%d", &tmp.x, &tmp.y);            Contain.push_back(tmp);        }        for(int i = n-1; i >= 0; i--) {            v.push_back(Contain[i]);        }        check.clear();        for(int i = 0; i < m; i++) {            scanf("%d%d", &tmp.x, &tmp.y);            check.push_back(tmp);        }        printf("Problem %d:\n", T++);        for(int i = 0; i < m; i++) {            int res = isPointIn(check[i]);            if(res==1) printf("Within\n");            else printf("Outside\n");        }    }}

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