Codeforces1307D 加边最短路最大化

n<=2e5
scanf printf比cin cout快5倍

autotoNumber = [&] (string const &s)->unsigned{…}

#include
using namespace std;
typedef long long ll;
const int maxn=2e5+5;
const int mod=1000;
const int INF=0x3f3f3f3f;
typedef pair<int,int> pii;
int t,n,m,k,ans,maxx;
string s;
vector<int> g[maxn];
int d1[maxn],d2[maxn];
bool keyv[maxn];	//打标记 
void bfs(int dist[],int s){
	dist[s]=0;
	queue<int> q;
	q.push(s);
	while(!q.empty()){
		int u=q.front();
		q.pop();
		for(int &v: g[u]){
			if(dist[v]==-1){
				q.push(v);
				dist[v]=dist[u]+1;
			}
		}
	}
}
int main(){
	scanf("%d %d %d",&n,&m,&k);
	for(int i=1;i<=k;i++){
		scanf("%d",&t);
		keyv[t]=true;
	}
	for(int i=1,u,v;i<=m;i++){
		scanf("%d%d",&u,&v);
		g[u].push_back(v);
		g[v].push_back(u);
	}
	
	memset(d1,-1,sizeof d1);
	memset(d2,-1,sizeof d2);
	
	bfs(d1,1);//1号点到其他点的最短路 
	bfs(d2,n);//n号点到其他点的最短路
	
	vector<pii> v;
	for(int i=1;i<=n;i++){	//k个没有用数组记录 
		if(keyv[i]){
//			v.push_back({d1[i],d2[i]});//1-i n-i最短路
			v.emplace_back(d1[i],d2[i]);
		}
	}
	sort(v.begin(),v.end(),[&](const pii &a,const pii &b){
		return a.first-a.second<b.first-b.second;
	});
	maxx=v[0].first;
	for(int i=1;i<v.size();i++){
		ans=max(ans,maxx+1+v[i].second);
		maxx=max(maxx,v[i].first);
	}
	printf("%d\n",min(ans,d1[n]));
	return 0;
}

链式向前星

#include 
using namespace std;
 
const int Maxn = 200005;
int n, m, k, ct, p1, p2, las, ans, cnt, a[Maxn], dis1[Maxn], dis2[Maxn], head[Maxn], from[Maxn], b[Maxn];
bool vis[Maxn], vis2[Maxn];
struct edg
{
	int nxt, to;
} edge[2 * Maxn];
void add(int x, int y)
{
	edge[++cnt] = (edg){head[x], y};
	head[x] = cnt;
}
queue <int> Qu;
void bfs(int dis[], int s)
{
	memset(dis, 0x3f, sizeof(int[n + 1]));
	dis[s] = 0;
	Qu.push(s);
	while (!Qu.empty())
	{
		int u = Qu.front();
		Qu.pop();
		for (int i = head[u]; i; i = edge[i].nxt)
		{
			int to = edge[i].to;
			if (dis[u] + 1 < dis[to])
			{
				dis[to] = dis[u] + 1;
				from[to] = u;
				Qu.push(to);
			}
		}
	}
}
int main()
{
	scanf("%d%d%d", &n, &m, &k);
	for (int i = 1; i <= k; i++)
		scanf("%d", &a[i]);
	for (int i = 1; i <= m; i++)
	{
		int x, y;
		scanf("%d%d", &x, &y);
		add(x, y);
		add(y, x);
	}
	bfs(dis1, 1);
	bfs(dis2, n);
	sort(a + 1, a + 1 + k, [](int x, int y){return dis1[x] < dis1[y];});
	for (int i = 2; i <= k; i++)
		ans = max(ans, min(dis1[n], 1 + dis1[a[i - 1]] + dis2[a[i]]));
	printf("%d", ans);
	return 0;
}