C :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define INF 1000000000

double G[110][110];
int axis[110][2];
int vis[110];
double d[110];
int n, m;
int A, B;

void dijkstra(){
memset(vis,0,sizeof(vis));
for(int i = 0;i <= n; i++)d[i] = INF;
d[A] = 0;
for(int i = 1;i <= n; i++){
    int u = -1, MIN = INF;
    for(int j = 1;j <= n; j++){
        if(vis[j]==0 && MIN > d[j]){
            u = j;
            MIN = d[j];
        }
    }
    if(u == B)return;
    vis[u] = 1;
    for(int v = 1;v <= n; v++){
        if(vis[v]==0 && G[u][v] != 0 && d[v] > d[u] + G[u][v]){
            d[v] = d[u] + G[u][v];
        }
    }
}
}

int main()
{
    while(scanf("%d",&n) != EOF){
        memset(G,0,sizeof(G));
        for(int i = 1;i <= n; i++){
            scanf("%d%d",&axis[i][0],&axis[i][1]);
        }
        scanf("%d",&m);
        while(m--){
            int a, b;
            scanf("%d%d",&a,&b);
            double dis = sqrt((axis[a][0]-axis[b][0])*(axis[a][0]-axis[b][0]) + \
                              (axis[a][1]-axis[b][1])*(axis[a][1]-axis[b][1]));
            G[a][b] = G[b][a] = dis;
        }
        scanf("%d%d",&A,&B);
        dijkstra();
        printf("%.2f\n",d[B]);
    }
    return 0;
}

C++ :

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;
double x[110],y[110],dis[101],a[101][101];
bool v[101];
int n,m,xx,yy,st,ed;
int q[10000];
inline double calc(int i,int j){
	return sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
}
void spfa(){
	memset(v,0,sizeof(v));
	for(int i=1;i<=n;++i) dis[i]=99999999.0;
	int l=1,r=1;
	q[1]=st;
	dis[st]=0;
	v[st]=true;
	while (l<=r){
		int x=q[l++];
		v[x]=false;
		for(int i=1;i<=n;++i)
		if (i!=x && a[x][i]<0x7fffffff)
			if (dis[i]>dis[x]+a[x][i]){
				dis[i]=dis[x]+a[x][i];
				if (!v[i]){
					v[i]=true;
					q[++r]=i;
				}
			}

	}
}
int main(){
	cin>>n;
	for(int i=1;i<=n;++i)
	  for(int j=1;j<=n;++j) a[i][j]=0x7fffffff;
	for(int i=1;i<=n;++i) a[i][i]=0;
	for(int i=1;i<=n;++i) scanf("%lf%lf",&x[i],&y[i]);
	cin>>m;
	for(int i=1;i<=m;++i){
		scanf("%d%d",&xx,&yy);
		if (xx!=yy)
			a[xx][yy]=a[yy][xx]=calc(xx,yy);
	}
	cin>>st>>ed;
	spfa();
	printf("%0.2lf",dis[ed]);
	return 0;
}