模板
1 #include <cstdio> 2 #include <queue> 3 #include <cstring> 4 #include <algorithm> 5 6 using namespace std; 7 8 int n, p, c, ans, cnt; 9 long long m; 10 struct node 11 { 12 int to, next; 13 }edge[5000001]; 14 int dis[5000001], head[500001], x, y; 15 bool vis[5000001]; 16 17 void spfa() 18 { 19 int i, j; 20 queue <int> q; 21 memset(dis, 0x7f, sizeof(dis)); 22 dis[c] = 1; 23 vis[c] = 1; 24 q.push(c); 25 while(!q.empty()) 26 { 27 i = q.front(); 28 q.pop(); 29 vis[i] = 0; 30 for(j = head[i]; j >= 0; j = edge[j].next) 31 if(dis[edge[j].to] > dis[i] + 1) 32 { 33 dis[edge[j].to] = dis[i] + 1; 34 if(!vis[edge[j].to]) 35 { 36 q.push(edge[j].to); 37 vis[edge[j].to] = 1; 38 } 39 } 40 } 41 } 42 43 int main() 44 { 45 int i, j; 46 scanf("%d %d %d", &n, &p, &c); 47 scanf("%d", &m); 48 memset(head, -1, sizeof(head)); 49 for(i = 1; i <= p; i++) 50 { 51 scanf("%d %d", &x, &y); 52 edge[cnt].to = y; 53 edge[cnt].next = head[x]; 54 head[x] = cnt++; 55 edge[cnt].to = x; 56 edge[cnt].next = head[y]; 57 head[y] = cnt++; 58 } 59 spfa(); 60 for(i = 1; i <= n; i++) ans = max(ans, dis[i]); 61 printf("%lld", ans + m); 62 return 0; 63 }
完事