【HDU】3656 Fire station

#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#define MAXN 5000
#define MAXM 60
#define INF 0x7FFFFFFF
using namespace std;
int n, m, size;
int L[MAXN], R[MAXN], U[MAXN], D[MAXN];
int H[MAXM], S[MAXM], C[MAXN], a[MAXN];
int dis[MAXM][MAXM];
bool vis[MAXM];
struct Point {
    int x, y;
};
Point p[MAXM];
int DIS(int i, int j) {
    int x, y;
    x = p[i].x - p[j].x;
    y = p[i].y - p[j].y;
    return x * x + y * y;
}
void Init() {
    int i;
    for (i = 0; i <= n; i++) {
        R[i] = i + 1;
        L[i + 1] = i;
        U[i] = D[i] = i;
        S[i] = 0;
        H[i] = -1;
    }
    R[n] = 0;
    size = n + 1;
}
void Link(int r, int c) {
    U[size] = c;
    D[size] = D[c];
    U[D[c]] = size;
    D[c] = size;
    if (H[r] < 0)
        H[r] = L[size] = R[size] = size;
    else {
        L[size] = H[r];
        R[size] = R[H[r]];
        L[R[H[r]]] = size;
        R[H[r]] = size;
    }
    S[c]++;
    C[size++] = c;
}
int A() {
    int i, j, k, res;
    memset(vis, false, sizeof(vis));
    for (res = 0, i = R[0]; i; i = R[i]) {
        if (vis[i])
            continue;
        res++;
        for (j = D[i]; j != i; j = D[j]) {
            for (k = R[j]; k != j; k = R[k])
                vis[C[k]] = true;
        }
    }
    return res;
}
void Remove(int c) {
    int i;
    for (i = D[c]; i != c; i = D[i]) {
        L[R[i]] = L[i];
        R[L[i]] = R[i];
    }
}
void Resume(int c) {
    int i;
    for (i = D[c]; i != c; i = D[i])
        L[R[i]] = R[L[i]] = i;
}
bool Dance(int now) {
    if (now + A() > m)
        return false;
    if (R[0] == 0)
        return true;
    int i, j, temp, c;
    for (temp = INF, i = R[0]; i; i = R[i]) {
        if (S[i] < temp) {
            temp = S[i];
            c = i;
        }
    }
    for (i = D[c]; i != c; i = D[i]) {
        Remove(i);
        for (j = R[i]; j != i; j = R[j])
            Remove(j);
        if (Dance(now + 1))
            return true;
        for (j = L[i]; j != i; j = L[j])
            Resume(j);
        Resume(i);
    }
    return false;
}
bool OK(int mid) {
    int i, j;
    Init();
    for (i = 1; i <= n; i++) {
        for (j = 1; j <= n; j++) {
            if (dis[i][j] <= mid)
                Link(i, j);
        }
    }
    return Dance(0);
}
int main() {
    int T, i, j, cnt;
    int high, low, mid;
    scanf("%d", &T);
    while (T--) {
        scanf("%d%d", &n, &m);
        for (i = 1; i <= n; i++)
            scanf("%d%d", &p[i].x, &p[i].y);
        for (cnt = 0, i = 1; i <= n; i++) {
            for (j = i; j <= n; j++)
                a[cnt++] = dis[i][j] = dis[j][i] = DIS(i, j);
        }
        sort(a, a + cnt);
        cnt = unique(a, a + cnt) - a;
        for (low = 0, high = cnt; low < high;) {
            mid = (low + high) >> 1;
            if (OK(a[mid]))
                high = mid;
            else
                low = mid + 1;
        }
        printf("%lf\n", sqrt((double) a[low]));
    }
    return 0;
}