rt，Floyd+并查集

#include<bits/stdc++.h>
using namespace std;
const int N = 1e2 + 55;
struct node
{
	int x, y;
}a[N];
int n, fa[N];
double g[N][N], ans = -1e9, maxi[N];
double get_dis(int x, int y)
{
	int dx = (abs(a[x].x - a[y].x)) * (abs(a[x].x - a[y].x));
	int dy = (abs(a[x].y - a[y].y)) * (abs(a[x].y - a[y].y));
	return sqrt(dx + dy);
}
int find(int x)
{
	if (fa[x] == x)
		return x;
	return fa[x] = find(fa[x]);
}
void merge(int x, int y)
{
	int fx = find(x), fy = find(y);
	if (fx == fy)
		return;
	fa[fy] = fx;
	return;
}
void floyd()
{
	for (int k = 1; k <= n; k++)
		for (int i = 1; i <= n; i++)
			for (int j = 1; j <= n; j++)
				g[i][j] = min(g[i][j], g[i][k] + g[k][j]);
	return;
}
int main()
{
	cin >> n;
	memset(g, 0x3f, sizeof(g));
	for (int i = 1; i <= n; i++)
		cin >> a[i].x >> a[i].y;
	for (int i = 1; i <= n; i++)
		g[i][i] = 0;
	for (int i = 1; i <= n; i++)
		fa[i] = i;
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++)
		{
			char c;
			cin >> c;
			if (c == '1')
			{
				double w = get_dis(i, j);
				g[i][j] = w;
				merge(i, j);
			}
		}
	floyd();
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++)
		{
			int fx = find(i), fy = find(j);
			if (fx == fy)
				maxi[fx] = max(maxi[fx], g[i][j]);
		}
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++)
		{
			int fx = find(i), fy = find(j);
			if (fx != fy)
			{
				double dis = get_dis(i, j);
				double mx = maxi[fx], my = maxi[fy];
				ans = max(ans, max(mx + my + dis, max(mx, my)));
			}
		}
	cout << fixed << setprecision(6) << ans;
	return 0;
}