HDU - 1007 平面最近点对

  1 #include <iostream>
  2 #include <fstream>
  3 #include <sstream>
  4 #include <cstdlib>
  5 #include <cstdio>
  6 #include <cmath>
  7 #include <string>
  8 #include <cstring>
  9 #include <algorithm>
 10 #include <queue>
 11 #include <stack>
 12 #include <vector>
 13 #include <set>
 14 #include <map>
 15 #include <list>
 16 #include <iomanip>
 17 #include <cctype>
 18 #include <cassert>
 19 #include <bitset>
 20 #include <ctime>
 21 
 22 using namespace std;
 23 
 24 #define pau system("pause")
 25 #define ll long long
 26 #define pii pair<int, int>
 27 #define pb push_back
 28 #define mp make_pair
 29 #define clr(a, x) memset(a, x, sizeof(a))
 30 
 31 const double pi = acos(-1.0);
 32 const int INF = 0x3f3f3f3f;
 33 const int MOD = 1e9 + 7;
 34 const double EPS = 1e-9;
 35 
 36 /*
 37 #include <ext/pb_ds/assoc_container.hpp>
 38 #include <ext/pb_ds/tree_policy.hpp>
 39 
 40 using namespace __gnu_pbds;
 41 tree<pli, null_type, greater<pli>, rb_tree_tag, tree_order_statistics_node_update> T;
 42 */
 43 
 44 struct point {
 45     double x, y;
 46     void input() {
 47         scanf("%lf%lf", &x, &y);
 48     }
 49     double dis(const point &p) {
 50         return sqrt((x - p.x) * (x - p.x) + (y - p.y) * (y - p.y));
 51     }
 52     bool operator < (const point &p) const {
 53         return x < p.x;}
 54 } p[100015], q[100015], p1[100015], p2[100015];
 55 int n;
 56 double dis;
 57 void mymerge(int s, int e) {
 58     if (s == e) return;
 59     int mi = s + e >> 1;
 60     mymerge(s, mi);
 61     mymerge(mi + 1, e);
 62     double d2 = p[mi].x + dis;
 63     double d1 = p[mi + 1].x - dis;
 64     int i = s, j = mi + 1, k = s, i1 = 1, i2 = 1;
 65     while (i <= mi && j <= e) {
 66         if (p[i].y < p[j].y) {
 67             if (d1 - EPS <= p[i].x && p[i].x <= d2 + EPS) {
 68                 p1[i1++] = p[i];
 69             }
 70             q[k++] = p[i++];
 71         }
 72         else {
 73             if (d1 - EPS <= p[j].x && p[j].x <= d2 + EPS) {
 74                 p2[i2++] = p[j];
 75             }
 76             q[k++] = p[j++];
 77         }
 78     }
 79     while (i <= mi) {
 80         if (d1 - EPS <= p[i].x && p[i].x <= d2 + EPS) {
 81             p1[i1++] = p[i];
 82         }
 83         q[k++] = p[i++];
 84     }
 85     while (j <= e) {
 86         if (d1 - EPS <= p[j].x && p[j].x <= d2 + EPS) {
 87             p2[i2++] = p[j];
 88         }
 89         q[k++] = p[j++];
 90     }
 91     for (int i = s; i <= e; ++i) p[i] = q[i];
 92     for (int i = 1, j = 1; i < i1 && j < i2; ++i) {
 93         while (j < i2 && p2[j].y < p1[i].y - dis) ++j;
 94         for (int k = j; k < i2 && p2[j].y < p1[i].y + dis; ++k) {
 95             double td = p1[i].dis(p2[j]);
 96             dis = min(dis, td);
 97         }
 98     }
 99 }
100 int main() {
101     while (~scanf("%d", &n) && n) {
102         for (int i = 1; i <= n; ++i) {
103             p[i].input();
104         }
105         sort(p + 1, p + n + 1);
106         dis = 1e18;
107         mymerge(1, n);
108         printf("%.2f\n", dis / 2);
109     }
110     return 0;
111 }