POJ 1389 Area of Simple Polygons

来源：互联网发布：ubuntu cinnamon 编辑：程序博客网时间：2024/06/07 18:31

扫描线

这次用的n^2算法，仍然是把x排序后扫描，每次算出两个相邻的x之间矩形的面积。当两矩形有重叠部分时把矩形升高，完全分开则分开算

#include<stdio.h>#include<algorithm>#include<math.h>using namespace std;typedef long long ll;struct square{    int x1,x2,y1,y2;};int cmp(square a,square b){    return a.y1<b.y1;}int main() {    #ifndef ONLINE_JUDGE    freopen("in.txt","r",stdin);    #endif // ONLINE_JUDGE    square s[1005];    int x[2005];    int left[2005],right[2005];    int x1,x2,y1,y2;    while(1){        int n=0;        int k=0;        while(1) {            scanf("%d%d%d%d",&x1,&y1,&x2,&y2);            if (x1==-1&&x2==-1 &&y1==-1&&y2==-1) break;            s[n].x1=x1; s[n].y1=y1; s[n].x2=x2; s[n++].y2=y2;            x[k++]=x1;  x[k++]=x2;        }        if(n==0) break;        sort(x,x+k);        sort(s,s+n,cmp);        ll area=0;        int m=0;        for(int i=0;i<k-1;i++){            if (x[i+1]-x[i]!=0){                left[m]=x[i]; right[m++]=x[i+1];            }        }        for(int i=0;i<m;i++){            int up=-1,down=-1;            for(int j=0;j<n;j++){                if (s[j].x1<=left[i] && right[i]<=s[j].x2) {                    if (s[j].y1>up){                        area+=(right[i]-left[i])*(up-down);                        up=s[j].y2; down=s[j].y1;                    }                    else if(s[j].y2>up){                        up=s[j].y2;                    }                }            }            area+=(right[i]-left[i])*(up-down);        }        printf("%I64d\n",area);    }}

0 0