HDU - 1392 凸包求周长(模板题)【Andrew】

<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[];
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[],a,b);
    if(m==)
        return dis(vex[],a)-dis(vex[],b)<=?true:false;
    else
        return m>?true:false;
}
node stackk[];
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!=){
        int i;
        for(i=;i<t;i++){
            scanf("%d%d",&vex[i].x,&vex[i].y);
        }
        if(t==)
            printf("%.2f\n",0.00);
        else if(t==)
            printf("%.2f\n",dis(vex[],vex[]));
        else{
            sort(vex,vex+t,cmp1);
            sort(vex+,vex+t,cmp);
            memset(stackk,,sizeof(stackk));
            stackk[]=vex[];
            stackk[]=vex[];
            int top=;
            for(i=;i<t;i++){
                while(i>=&&cross(stackk[top-],stackk[top],vex[i])<)
                    top--;
                stackk[++top]=vex[i];
            }
            double s=;
            for(i=;i<=top;i++)
                s+=dis(stackk[i-],stackk[i]);
            s+=dis(stackk[top],vex[]);
            printf("%.2f\n",s);
        }
    }
}

2018-08-22