1. 程式人生 > >平面最近點對(nlogn)

平面最近點對(nlogn)

#include <bits/stdc++.h>
using namespace std;
const int N = 2e5+1000;
struct P{
    double x, y; //此處修改int
    bool operator <(P B)const { return x < B.x; }
}p[N];
double dis(P A, P B) { return sqrt((A.x-B.x)*(A.x-B.x) + (A.y-B.y)*(A.y-B.y)); } //此處修改int
P Q[N];
double Divide(int l, int r)
{ if(l == r) return 1e9; int mid = (l+r)>>1, tot = 0; double d,tx = p[mid].x; //此處修改int d = min(Divide(l, mid), Divide(mid+1, r)); for(int i = l, j = mid+1; (i <= mid || j <= r); i++){ while(j <= r && (p[i].y > p[j].y || i > mid)) Q[tot++] = p[j]
, j++; //歸併按y排序 if(fabs(p[i].x - tx) < d && i <= mid){ //選擇中間符合要求的點 for(int k = j-1; k > mid && j-k < 3; k--) d = min(d, dis(p[i], p[k])); for(int k = j; k <= r && k-j < 2; k++) d = min(d, dis(p[i], p[k])); } if(i <=
mid) Q[tot++] = p[i]; } for(int i = l, j = 0; i <= r; i++, j++) p[i] = Q[j]; return d; } int main() { freopen("a.txt","r",stdin); int n; cin>>n; for(int i = 1; i <= n; i++) cin>>p[i].x>>p[i].y; sort(p+1, p+1+n); printf("%.4f",Divide(1, n)); }