P4423 [BJWC2011]最小三角形

#include"stdio.h"
#include"string.h"
#include"vector"
#include"math.h"
#include"algorithm"
using namespace std;

typedef struct Node{
    double x,y;
    int id;
}Node;

int n;
Node node[200100];
Node tran[200100];
double minx = 1e20;

bool same(double a, double b) { /// 1e-5精度意义下的浮点数相等
    if(fabs(a-b) <= 1e-5) return true; return false;
}
int cmpx(Node a,Node b){
      if(!same(a.x, b.x)) return a.x<b.x; return a.y<b.y;
}
int cmpy(Node a,Node b){
     if(!same(a.y, b.y)) return a.y<b.y; return a.x<b.x;
}

void dist_minx(Node a,Node b,Node c){
    double s1 = sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
    double s2 = sqrt((a.x - c.x) * (a.x - c.x) + (a.y - c.y) * (a.y - c.y));
    double s3 = sqrt((b.x - c.x) * (b.x - c.x) + (b.y - c.y) * (b.y - c.y));
    minx = min(minx,s1 + s2 + s3);
}

void merge_node(int l,int mid,int r)
{
    int t = 0;
    int i = l,j = mid + 1;
    while(i <= mid && j <= r)
    {
        if(node[i].y < node[j].y)
        {
            tran[++ t] = node[i]; i ++; continue;
        } else {
            tran[++ t] = node[j]; j ++; continue;
        }
    }
    while(i <= mid) tran[++ t] = node[i ++];
    while(j <= r) tran[++ t] = node[j ++];
    for(int i = l; i <= r; i ++)
        node[i] = tran[i - l + 1];
}

void Blocking(int l,int r)
{
    if(r - l <= 4)
    {
        for(int i = l; i < r; i ++)
        {
            for(int j = i + 1; j <= r; j ++)
            {
                for(int k = j + 1; k <= r; k ++)
                  dist_minx(node[i],node[j],node[k]);
            }
        }
        sort(node + l,node + r + 1,cmpy);
        return ;
    }

    int mid = (l + r) >> 1;
    double midx = node[mid].x;
    Blocking(l,mid); Blocking(mid + 1,r);
    merge_node(l,mid,r);

    vector<Node> Q;
    for(int i = l; i <= r; i ++)
    {
        if(fabs(node[i].x - midx) >= minx / 2) continue;
        for(int j = Q.size() - 1; j >= 0; j --)
        {
            if(fabs(Q[j].y - node[i].y) >= minx) break;
            for(int k = j - 1; k >= 0; k --)
              dist_minx(Q[j],node[i],Q[k]);
        }
        Q.push_back(node[i]);
    }
    Q.clear();
    return ;
}

int main()
{
    scanf("%d",&n);
    for(int i = 1; i <= n; i ++)
    {
        scanf("%lf%lf",&node[i].x,&node[i].y);
        node[i].id = i;
    }
    sort(node + 1,node + n + 1,cmpx);
    Blocking(1,n);
    printf("%0.6lf\n",minx);
}