POJ3714(分治)

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题意是给你两堆点，求毎堆点各取一个的最近距离。

给毎个点一个属于标记，然后合并的时候判断是不是属于不同的两堆点。

#include <cstdio>#include <cmath>#include <algorithm>using namespace std;#define maxn 211111#define INF 1e15struct node {    double x, y;    bool belong;} p[maxn], tmp[maxn];int n;bool cmp1 (const node &a, const node &b) {    return a.x < b.x || (a.x == b.x && a.y < b.y);}bool cmp2 (const node &a, const node &b) {    return a.y < b.y;}double dis (node a, node b) {    double xx = a.x-b.x, yy = a.y-b.y;    return sqrt (xx*xx + yy*yy);}double solve (int l, int r) {    double d = INF;    if (l == r)        return d;    if (r-l == 1) {        if (p[l].belong^p[r].belong)            return dis (p[l], p[r]);        else            return d;    }    int mid = (l+r)>>1;    d = min (solve (l, mid), solve (mid+1, r));    int cnt = 0;    for (int i = l; i <= r; i++) {        if (fabs (p[mid].x-p[i].x) < d) {            tmp[cnt++] = p[i];        }    }    sort (tmp, tmp+cnt, cmp2);    for (int i = 0; i < cnt; i++) {        for (int j = i+1; j < cnt && tmp[j].y-tmp[i].y < d; j++) {            if (tmp[i].belong^tmp[j].belong)                d = min (d, dis(tmp[i], tmp[j]));        }    }    return d;}int main () {    //freopen ("in", "r", stdin);    int t;    scanf ("%d", &t);    while (t--) {        scanf ("%d", &n);        for (int i = 0; i < n; i++) {            scanf ("%lf%lf", &p[i].x, &p[i].y);            p[i].belong = 0;        }        for (int i = n; i < n+n; i++) {            scanf ("%lf%lf", &p[i].x, &p[i].y);            p[i].belong = 1;        }        n <<= 1;        sort (p, p+n, cmp1);        printf ("%.3f\n", solve (0, n-1));    }    return 0;}

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