# 【題解】Codeforces 1307D. Cow and Fields

【題目敘述】http://codeforces.com/contest/1307/problem/D
【解題想法】BFS

```#include <iostream>
#include <vector>
#include <queue>
#include <cstring>
#include <algorithm>
using namespace std;

int n, m, k, s[200005], t[200005], x, y;
vector <int> a;
vector <int> v[200005];

bool cmp(int x, int y){
if (s[x]-t[x] != s[y]-t[y]) return s[x]-t[x] < s[y]-t[y];
else return x < y;
}

int main() {
cin >> n >> m >> k;
for (int i = 0; i < k; i++){
cin >> x;
a.push_back(x);
}
for (int i = 0; i < m; i++){
cin >> x >> y;
v[x].push_back(y);
v[y].push_back(x);
}
queue <int> q;
memset(s, -1, sizeof(s));
q.push(1);
s[1] = 0;
while (!q.empty()){
x = q.front();
q.pop();
for (int i:v[x]){
if(s[i] == -1){
s[i] = s[x]+1;
q.push(i);
}
}
}
memset(t, -1, sizeof(t));
q.push(n);
t[n] = 0;
while (!q.empty()){
x = q.front();
q.pop();
for (int i:v[x]){
if(t[i] == -1){
t[i] = t[x]+1;
q.push(i);
}
}
}
sort(a.begin(), a.end(), cmp);
int ans = 0, mx = s[a[0]];
for (int i = 1; i < k; i++){
ans = max(ans, mx+t[a[i]]+1);
mx = max(mx, s[a[i]]);
}
ans = min(ans, s[n]);
cout << ans << "\n";
}
```