题目链接:
http://hihocoder.com/problemset/problem/1224
题意:
题解:
首先我们先dfs出最长链,然后我们再dfs出每一个点能够最长延展多少
然后最后答案就是最长链的长度+最长延展多少就好了
代码:
1 #include <bits/stdc++.h> 2 using namespace std; 3 typedef long long ll; 4 #define MS(a) memset(a,0,sizeof(a)) 5 #define MP make_pair 6 #define PB push_back 7 const int INF = 0x3f3f3f3f; 8 const ll INFLL = 0x3f3f3f3f3f3f3f3fLL; 9 inline ll read(){ 10 ll x=0,f=1;char ch=getchar(); 11 while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} 12 while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} 13 return x*f; 14 } 15 ////////////////////////////////////////////////////////////////////////// 16 const int maxn = 1e5+10; 17 18 vector<int> G[maxn]; 19 int d[maxn],vis[maxn],fa[maxn]; 20 21 void dfs(int x,int deep){ 22 d[x] = deep; 23 for(auto v : G[x]){ 24 if(vis[v]) continue; 25 26 fa[v] = x; 27 dfs(v,deep+1); 28 } 29 } 30 31 int main(){ 32 int n=read(); 33 for(int i=1; i<n; i++){ 34 int u=read(),v=read(); 35 G[u].push_back(v); 36 } 37 dfs(1,0); 38 39 int bf=1,ans1 = 0; 40 for(int i=1; i<=n; i++){ 41 if(d[i] > ans1){ 42 ans1 = d[i]; 43 bf = i; 44 } 45 } 46 47 while(bf != 1){ 48 vis[bf] = 1; 49 bf = fa[bf]; 50 } 51 vis[1] = 1; 52 53 for(int i=1; i<=n; i++){ 54 if(vis[i]) 55 dfs(i,0); 56 } 57 58 int ans2 = 0; 59 for(int i=1; i<=n; i++) 60 if(!vis[i]) 61 ans2 = max(d[i],ans2); 62 63 cout << ans1+ans2 << endl; 64 65 return 0; 66 }