51nod 1649 齐头并进(Codeforces 601A The Two Routes) (最短路)

#include <bits/stdc++.h>
#define maxm 200005
#define maxn 405
#define inf 0x3f3f3f3f
using namespace std;
struct Node{
	int to,w,next;
	bool operator < (const Node &a) const {
		return a.w < w;
	}
}Edge[maxm],S,Next;
int head[maxm],num;
int dist[maxm];
bool a[maxn][maxn],vis[maxm];
int n,m;

void init(){
	for(int i=0;i<=n;i++){
		head[i] = -1;
	}
	num = 0;
}

void add(int u,int v){
	Edge[num].w = 1;
	Edge[num].to = v;
	Edge[num].next = head[u];
	head[u] = num ++;
}

void dijkstra(int s){
	for(int i=0;i<=n;i++){
		dist[i] = inf;
		vis[i] = false;
	}
	priority_queue<Node> q;
	S.to = s;
	dist[s] = 0;
	q.push(S);
	while(!q.empty()){
		int u = q.top().to;
		q.pop();
		if(vis[u]) continue;
		vis[u] = true;
		for(int i=head[u];i!=-1;i=Edge[i].next){
			int v = Edge[i].to;
			if(!vis[v] && dist[v] > dist[u] + Edge[i].w){
				dist[v] = dist[u] + Edge[i].w;
				Next.to = v;
				Next.w = dist[v];
				q.push(Next);
			}
		}
	}
}

int main()
{
	// init();
	scanf("%d%d",&n,&m);
	init();
	for(int i=0;i<m;i++){
		int u,v;
		scanf("%d%d",&u,&v);
		a[u][v] = a[v][u] = true;
		add(u, v);
		add(v, u);
	}
	dijkstra(1);
	int ans1 = dist[n];
	init();
	for(int i=1;i<=n;i++){
		for(int j=i+1;j<=n;j++){
			if(a[i][j] == false){
				add(i, j);
				add(j, i);
			}
		}
	}
	dijkstra(1);
	int ans2 = dist[n];
	printf("%d\n",max(ans1, ans2) == inf ? -1 : max(ans1, ans2));
	return 0;
}