HDU

<题目链接>

题目大意：

给出一些点，让你求出将这些点全部围住需要的多长的绳子。

Andrew算法

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
struct node{
    int x,y;
};
node vex[1000];
bool cmp1(node a,node b){
    if(a.y==b.y)
        return a.x<b.x;
    else
        return a.y<b.y;
}
int cross(node,node,node);
double dis(node,node);
bool cmp(node a,node b){
    int m=cross(vex[0],a,b);
    if(m==0)
        return dis(vex[0],a)-dis(vex[0],b)<=0?true:false;
    else
        return m>0?true:false;
}
node stackk[1000];
int cross(node a,node b,node c){
    return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);
}
double dis(node a,node b){
    return sqrt((a.x-b.x)*(a.x-b.x)*1.0+(a.y-b.y)*(a.y-b.y));
}
int main(){
    int t;
    while(scanf("%d",&t),t!=0){
        int i;
        for(i=0;i<t;i++){
            scanf("%d%d",&vex[i].x,&vex[i].y);
        }
        if(t==1)
            printf("%.2f
",0.00);
        else if(t==2)
            printf("%.2f
",dis(vex[0],vex[1]));
        else{
            sort(vex,vex+t,cmp1);
            sort(vex+1,vex+t,cmp);
            memset(stackk,0,sizeof(stackk));
            stackk[0]=vex[0];
            stackk[1]=vex[1];
            int top=1;
            for(i=2;i<t;i++){
                while(i>=1&&cross(stackk[top-1],stackk[top],vex[i])<0)
                    top--;  
                stackk[++top]=vex[i]; 
            }
            double s=0;
            for(i=1;i<=top;i++)
                s+=dis(stackk[i-1],stackk[i]);
            s+=dis(stackk[top],vex[0]);
            printf("%.2f
",s);
        }
    }
}

2018-08-22