Floyd

https://www.acwing.com/problem/content/1127/

#include <bits/stdc++.h>
using namespace std;
#define IO ios::sync_with_stdio(false);cin.tie(0); cout.tie(0)
inline int lowbit(int x) { return x & (-x); }
#define ll long long
#define pb push_back
#define PII pair<int, int>
#define x first
#define y second
#define inf 0x3f3f3f3f
const double INF = 1e20;
const int N = 155;
typedef pair<double, double> PDD;
int n;
PDD q[N];
double d[N][N];
double maxd[N];
char g[N][N];

double get_dist(PDD a, PDD b) {
    double dx = a.x - b.x;
    double dy = a.y - b.y;
    return sqrt(dx * dx + dy * dy);
}

int main() {
    IO;
    cin >> n;
    for (int i = 0; i < n; ++i) cin >> q[i].x >> q[i].y;
    for (int i = 0; i < n; ++i) cin >> g[i];

    for (int i = 0; i < n; ++i) 
        for (int j = 0; j < n; ++j)
            if (i == j) d[i][j] = 0;
            else if (g[i][j] == '1') d[i][j] = get_dist(q[i], q[j]);
            else d[i][j] = INF;
   
    for (int k = 0; k < n; ++k) 
        for (int i = 0; i < n; ++i)
            for (int j = 0; j < n; ++j)
                d[i][j] = min(d[i][j], d[i][k] + d[k][j]);

    double r1 = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j)
            if (d[i][j] < INF / 2)
                maxd[i] = max(maxd[i], d[i][j]);
        r1 = max(r1, maxd[i]);
    }

    double r2 = INF;
    for (int i = 0; i < n; ++i)
        for (int j = 0; j < n; ++j)
            if (d[i][j] > INF / 2)
                r2 = min(r2, maxd[i] + maxd[j] + get_dist(q[i], q[j]));

    printf("%.6lf\n", max(r1, r2));
    return 0;
}