HDU-4607 Park Visit bfs | DP | dfs

　　题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4607

　　首先考虑找一条最长链长度k，如果m<=k+1，那么答案就是m。如果m>k+1，那么最长链上还有其他分支，来回走一遍，因此答案为2*m-k-1。。。求最长链可以DP，两次BFS或者DFS等。。

  1 //STATUS:C++_AC_453MS_3524KB

  2 #include <functional>

  3 #include <algorithm>

  4 #include <iostream>

  5 //#include <ext/rope>

  6 #include <fstream>

  7 #include <sstream>

  8 #include <iomanip>

  9 #include <numeric>

 10 #include <cstring>

 11 #include <cassert>

 12 #include <cstdio>

 13 #include <string>

 14 #include <vector>

 15 #include <bitset>

 16 #include <queue>

 17 #include <stack>

 18 #include <cmath>

 19 #include <ctime>

 20 #include <list>

 21 #include <set>

 22 #include <map>

 23 using namespace std;

 24 //using namespace __gnu_cxx;

 25 //define

 26 #define pii pair<int,int>

 27 #define mem(a,b) memset(a,b,sizeof(a))

 28 #define lson l,mid,rt<<1

 29 #define rson mid+1,r,rt<<1|1

 30 #define PI acos(-1.0)

 31 //typedef

 32 typedef __int64 LL;

 33 typedef unsigned __int64 ULL;

 34 //const

 35 const int N=100010;

 36 const LL INF=0x3f3f3f3f;

 37 const int MOD=1000000007,STA=8000010;

 38 const LL LNF=1LL<<60;

 39 const double EPS=1e-8;

 40 const double OO=1e15;

 41 const int dx[4]={-1,0,1,0};

 42 const int dy[4]={0,1,0,-1};

 43 const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};

 44 //Daily Use ...

 45 inline int sign(double x){return (x>EPS)-(x<-EPS);}

 46 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}

 47 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}

 48 template<class T> inline T lcm(T a,T b,T d){return a/d*b;}

 49 template<class T> inline T Min(T a,T b){return a<b?a:b;}

 50 template<class T> inline T Max(T a,T b){return a>b?a:b;}

 51 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}

 52 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}

 53 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}

 54 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}

 55 //End

 56 

 57 struct Edge{

 58     int u,v;

 59 }e[N*2];

 60 int first[N],next[N*2],d[N];

 61 int Ca,T,n,m,mt;

 62 

 63 void adde(int a,int b)

 64 {

 65     e[mt].u=a;e[mt].v=b;

 66     next[mt]=first[a];first[a]=mt++;

 67     e[mt].u=b;e[mt].v=a;

 68     next[mt]=first[b];first[b]=mt++;

 69 }

 70 

 71 int bfs(int s)

 72 {

 73     int u,i,hig;

 74     mem(d,0);

 75     d[s]=1;

 76     queue<int> q;

 77     q.push(s);

 78     hig=-1;

 79     while(!q.empty())

 80     {

 81         u=q.front();q.pop();

 82         for(i=first[u];i!=-1;i=next[i]){

 83             if(!d[e[i].v]){

 84                 d[e[i].v]=d[e[i].u]+1;

 85                 if(d[e[i].v]>hig){

 86                     hig=d[e[i].v];

 87                     T=e[i].v;

 88                 }

 89                 q.push(e[i].v);

 90             }

 91         }

 92     }

 93     return hig;

 94 }

 95 

 96 int main()

 97 {

 98  //   freopen("in.txt","r",stdin);

 99     int i,j,a,b,hig;

100     scanf("%d",&Ca);

101     while(Ca--)

102     {

103         scanf("%d%d",&n,&m);

104         mem(first,-1);mt=0;

105         for(i=1;i<n;i++){

106             scanf("%d%d",&a,&b);

107             adde(a,b);

108         }

109         bfs(1);

110         hig=bfs(T);

111 

112         while(m--){

113             scanf("%d",&a);

114             if(a>hig){

115                 printf("%d\n",2*a-hig-1);

116             }

117             else printf("%d\n",a-1);

118         }

119     }

120     return 0;

121 }