题意:问给定的一张图中,相距最远的两个点的距离为多少。
解法:跟求树的直径差不多,从1 开始bfs,得到一个最远的点,然后再从该点bfs一遍,得到的最长距离即为答案。
代码:
#include <iostream> #include <cstdio> #include <cstring> #include <cstdlib> #include <cmath> #include <algorithm> #include <string> #include <vector> #include <queue> #include <map> using namespace std; #define N 100007 map<string,int> mp; vector<int> G[1006]; int vis[1006],n,m,Maxdis,Maxtag; struct node{ int dis,u; }; void dfs(int u) { vis[u] = 1; for(int i=0;i<G[u].size();i++) { int v = G[u][i]; if(!vis[v]) dfs(v); } } void bfs(int u) { queue<node> que; memset(vis,0,sizeof(vis)); node now; now.dis = 0; now.u = u; que.push(now); vis[u] = 1; while(!que.empty()) { int SZ = que.size(); while(SZ--) { node tmp = que.front(); que.pop(); int dis = tmp.dis; int u = tmp.u; if(dis > Maxdis) { Maxdis = dis; Maxtag = u; } for(int i=0;i<G[u].size();i++) { int v = G[u][i]; if(!vis[v]) { now.u = v; now.dis = dis+1; vis[v] = 1; que.push(now); } } } } } int main() { int i,j; string S; while(scanf("%d",&n)!=EOF && n) { mp.clear(); for(i=1;i<=n;i++) { cin>>S; mp[S] = i; G[i].clear(); } scanf("%d",&m); string A,B; for(i=1;i<=m;i++) { cin>>A>>B; int a = mp[A], b = mp[B]; G[a].push_back(b); G[b].push_back(a); } memset(vis,0,sizeof(vis)); dfs(1); int Link = 1; for(i=1;i<=n;i++) if(!vis[i]) Link = 0; if(!Link) { puts("-1"); continue; } Maxdis = 0, Maxtag = -1; bfs(1); int S = Maxtag; Maxdis = 0, Maxtag = -1; bfs(S); printf("%d\n",Maxdis); } return 0; }
时间: 2024-10-28 00:53:48