HDU4607+BFS

 1 /*

 2 bfs+求树的直径

 3 关键：if k<=maxs+1 直接输出k-1；

 4     else： k肯定的是包括最长路。先从最长路的起点出发，再走分支，最后到达最长路的终点。

 5             因此是2*(k-(maxs+1))+maxs;

 6 */

 7 #include<stdio.h>

 8 #include<string.h>

 9 #include<stdlib.h>

10 #include<algorithm>

11 #include<iostream>

12 #include<queue>

13 #include<map>

14 #include<math.h>

15 using namespace std;

16 typedef long long ll;

17 //typedef __int64 int64;

18 const int maxn = 100005;

19 const int inf = 0x7fffffff;

20 const double pi=acos(-1.0);

21 const double eps = 1e-8;

22 struct Node{

23     int v,next;

24 }edge[ maxn<<1 ];

25 int cnt,head[ maxn ];

26 int vis[ maxn ],dis[ maxn ];

27 int maxs,maxNode;

28 void init(){

29     cnt = 0;

30     memset( head,-1,sizeof( head ) );

31 }

32 void addedge( int a,int b ){

33     edge[ cnt ].v = b;

34     edge[ cnt ].next = head[ a ];

35     head[ a ] = cnt++;

36     

37     edge[ cnt ].v = a;

38     edge[ cnt ].next = head[ b ];

39     head[ b ] = cnt++;

40 }

41 void bfs( int s,int n ){

42     memset( vis,0,sizeof( vis ) );

43     vis[ s ] = 1;

44     queue<int>q;

45     q.push( s );

46     //for( int i=0;i<=n;i++ )

47         //dis[ i ] = inf;

48     dis[ s ] = 0;

49     maxs = 0;

50     while( !q.empty() ){

51         int cur = q.front();

52         q.pop();

53         if( dis[ cur ]>maxs ){

54             maxs = dis[ cur ];

55             maxNode = cur;

56         }

57         //maxs = max( maxs,dis[ cur ] );

58         for( int i=head[ cur ];i!=-1;i=edge[ i ].next ){

59             int v = edge[ i ].v;

60             if( vis[ v ]==1 ) continue;

61             vis[ v ] = 1;

62             dis[ v ] = dis[ cur ]+1;

63             q.push( v );

64         }    

65     }

66     return ;

67 }

68 int main(){

69     int T;

70     scanf("%d",&T);

71     while( T-- ){

72         int n,m;

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

74         int a,b;

75         init();

76         int N = n-1;

77         while( N-- ){

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

79             addedge( a,b );

80         }

81         bfs( 1,n );

82         bfs( maxNode,n );

83         //maxs=the R of the tree

84         while( m-- ){

85             scanf("%d",&b);

86             if( b<=maxs+1 ) printf("%d\n",b-1);

87             else printf("%d\n",2*(b-maxs-1)+maxs);

88         }

89     }

90     return 0;

91 }

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