刚学。。。

#include <iostream>
#include <queue>
#include <vector>
#include <cmath>
#include <cstdio>
using namespace std;

const int N = 1e3 + 5;
int n, m, start, ende;
double dista[N];
bool isin[N];

struct Node
{
	int place;
	double qz;
};

struct ZB
{
	int x, y;
};

ZB arr[N];
vector<Node> vec[N];

double dist(const ZB& a, const ZB& b)
{
	return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

void add_edge(int a, int b)
{
	Node tmp;
	tmp.place = b; 
	tmp.qz = dist(arr[a], arr[b]);
	vec[a].push_back(tmp);
}

void Init()
{
	for (int i = 0; i < N; i++)
	{
		dista[i] = 1e15;
	}
}

void spfa(int g)
{
	queue<int> q;
	q.push(g);
	isin[g] = true;
	while (!q.empty())
	{
		int temp = q.front();
		q.pop();
		isin[temp] = false;
		for (int i = 0; i < vec[temp].size(); i++)
		{
			Node as = vec[temp][i];
			if (dista[as.place] > dista[temp] + as.qz)
			{
				dista[as.place] = dista[temp] + as.qz;
				if (!isin[as.place])
				{
					isin[as.place] = true;
					q.push(as.place);
				}
			}
		}
	}
}

int main()
{
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		cin >> arr[i].x >> arr[i].y;
	}
	cin >> m;
	for (int i = 1; i <= m; i++)
	{
		int o, l;
		cin >> o >> l;
		add_edge(o, l);
		add_edge(l, o);
	}
	cin >> start >> ende;
	Init();
	spfa(start);
	printf("%.2lf", dista[ende]);
	return 0;
}