Travel

The country frog lives in has?nn?towns which are conveniently numbered by?1,2,…,n1,2,…,n.

Among?n(n?1)2n(n?1)2?pairs of towns,?mm?of them are connected by bidirectional highway, which needs?aa?minutes to travel. The other pairs are connected by railway, which needs?bb?minutes to travel.

Find the minimum time to travel from town?11?to town?nn.

Input

The input consists of multiple tests. For each test:

The first line contains?44?integers?n,m,a,bn,m,a,b?(2≤n≤105,0≤m≤5?105,1≤a,b≤1092≤n≤105,0≤m≤5?105,1≤a,b≤109). Each of the following?mmlines contains?22?integers?ui,viui,vi, which denotes cities?uiui?and?vivi?are connected by highway. (1≤ui,vi≤n,ui≠vi1≤ui,vi≤n,ui≠vi).

Output

For each test, write?11?integer which denotes the minimum time.

Sample Input

    3 2 1 31 22 33 2 2 31 22 3

Sample Output

    23

題意:有n個城市,編號為1~n,每個城市都相互連通,其中有m對城市通過公路連通,其他的城市通過鐵路連通,經過公路的時間為a,
經過鐵路的時間為b,問從1到達n的時間最短為多少.

#include<iostream>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<map>
#include<queue>
#include<vector>
#define  ll long long
using namespace std;
int n,m;
ll a,b;
vector<int>v[100005];
struct node
{int v;ll t;
};
queue<node>q;
bool bo[100005];
ll min1(ll a,ll b)
{if(a>b)return b;return a;
}
int main()
{while(~scanf("%d %d %lld %lld",&n,&m,&a,&b)){while(!q.empty()) q.pop();for(ll i=0;i<100005;i++) v[i].clear();memset(bo,0,sizeof(bo));bool bb=0;for(ll i=1;i<=m;i++){int x,y;scanf("%d %d",&x,&y);v[x].push_back(y);v[y].push_back(x);if((x==1&&y==n)||(x==n&&y==1))bb=1;//可能高速比公路慢}if(a>=b){//挑出與n沒有高速公路的點中存不存在與1也沒有高速公路的點if(bb==0)printf("%d\n",b);else{for(int i=2;i<n;i++){bool is=0;for(int j=0;j<v[i].size();j++){if(v[i][j]==1||v[i][j]==n)is=1;}if(is==0){bb=0;break;}}if(bb==0)printf("%d\n",min(a,2*b));else printf("%d\n",a);}continue;}node s;s.v=1;s.t=0;q.push(s);ll mx=b;bo[1]=1;bool f=0;while(!q.empty()){node s;s=q.front();q.pop();for(int i=0;i<v[s.v].size();i++){int y=v[s.v].at(i);if(bo[y]) continue;if(y==n){mx=min1(mx,(s.t+1)*a);f=1;break;}node ss;ss.t=s.t+1;ss.v=y;q.push(ss);}if(f)break;}printf("%lld\n",mx);}return 0;
}

?

轉載于:https://www.cnblogs.com/caiyishuai/p/8955140.html

總結

以上是生活随笔為你收集整理的四川第七届 I Travel（bfs）的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。