BFS 判断可达性 邻接vector存储
1 # include <iostream> 2 # include <algorithm> 3 # include <queue> 4 # include <string.h> 5 # include <vector> 6 # define N 1010 7 using namespace std; 8 9 bool vis[N]; 10 vector<int>G[N]; 11 12 void add(int u, int v) 13 { 14 G[u].push_back(v); 15 } 16 17 bool BFS(int s) 18 { 19 queue<int>q; 20 q.push(s); 21 vis[s] = true; 22 while(!q.empty()) 23 { 24 int u = q.front(); 25 vis[u] = true; 26 q.pop(); 27 for(int i = 0; i < (int)G[u].size(); i++) 28 { 29 int v = G[u][i]; 30 if(!vis[v]) 31 { 32 q.push(v); 33 vis[v] = true; 34 if(v == 1) 35 return true; 36 } 37 } 38 } 39 return false; 40 } 41 42 int main(void) 43 { 44 int n, m; 45 while(cin >> n >> m) 46 { 47 memset(vis, 0, sizeof(vis)); 48 for(int i = 0; i <= n; i++) 49 G[i].clear(); 50 for(int i = 0; i < m; i++) 51 { 52 int u, v; 53 cin >> u >> v; 54 add(u, v); 55 } 56 if(BFS(n)) 57 cout << "YES" << endl; 58 else 59 cout << "NO" << endl; 60 } 61 62 return 0; 63 }
BFS 从起始点到目标点的最短步数 邻接vector存储
1 # include <iostream> 2 # include <algorithm> 3 # include <queue> 4 # include <string.h> 5 # include <vector> 6 # define N 1010 7 using namespace std; 8 9 bool vis[N]; 10 vector<int>G[N]; 11 12 struct node 13 { 14 int v, cnt; 15 } ; 16 17 void add(int u, int v) 18 { 19 G[u].push_back(v); 20 } 21 22 int BFS(int s) 23 { 24 queue<node>q; 25 node p; 26 p.v = s; 27 p.cnt = 0; 28 q.push(p); 29 vis[s] = true; 30 while(!q.empty()) 31 { 32 node u = q.front(); 33 vis[u.v] = true; 34 q.pop(); 35 if(u.v == 1) 36 return u.cnt; 37 for(int i = 0; i < (int)G[u.v].size(); i++) 38 { 39 node k; 40 k.v = G[u.v][i]; 41 k.cnt = u.cnt+1; 42 if(!vis[k.v]) 43 { 44 q.push(k); 45 vis[k.v] = true; 46 } 47 } 48 } 49 return 0; 50 } 51 52 int main(void) 53 { 54 int n, m; 55 while(cin >> n >> m) 56 { 57 memset(vis, 0, sizeof(vis)); 58 for(int i = 0; i <= n; i++) 59 G[i].clear(); 60 for(int i = 0; i < m; i++) 61 { 62 int u, v; 63 cin >> u >> v; 64 add(u, v); 65 } 66 int t = BFS(n); 67 if(!t) 68 cout << "NO" << endl; 69 else 70 cout << t << endl; 71 } 72 73 return 0; 74 }