The Two Routes CodeForces - 601A（水最短路）

一个完全图

1和n肯定有一条路  不是公路就是铁路  另=

另一个跑遍最短路即可

#include <bits/stdc++.h>
#define mem(a, b) memset(a, b, sizeof(a))
using namespace std;
const int maxn = 100100, INF = 0x7fffffff;
int head[maxn], cnt, n, m;
int vis[maxn], d[maxn];
bool w[500][500];
struct node
{int u, v, next;
}Node[maxn<<1];void add_(int u, int v)
{Node[cnt].u = u;Node[cnt].v = v;Node[cnt].next = head[u];head[u] = cnt++;
} 
void add(int u, int v)
{add_(u, v);add_(v, u);
}void spfa(int s)
{queue<int> Q;for(int i=0; i<=n; i++) d[i] = INF;mem(vis, 0);Q.push(s);vis[s] = 1;d[s] = 0;while(!Q.empty()){int u = Q.front(); Q.pop();vis[u] = 0;for(int i=head[u]; i!=-1; i=Node[i].next){node e = Node[i];if(d[e.v] > d[u] + 1){d[e.v] = d[u] + 1;if(!vis[e.v]){vis[e.v] = 1;Q.push(e.v); }}}} 
}int main()
{mem(head, -1);cnt = 0;cin>> n >> m;int u, v, flag = 0;for(int i=0; i<m; i++){scanf("%d%d", &u, &v);if(u == 1 && v == n || u == n && v == 1)flag = 1;w[u][v] = w[v][u] = 1;add(u, v);}if(flag){mem(head, -1);cnt = 0;for(int i=1; i<=n; i++){for(int j=i+1; j<=n; j++){if(!w[i][j])add(i, j);}}}//    cout<< "111" <<endl;spfa(1);if(d[n] == INF){cout<< "-1" <<endl;return 0;}cout<< d[n] <<endl;return 0;
}