PKU1330+LCA

简单的LCA。。。

dfs里fa的判断很重要呀。。。亲。。。

 1 /*

 2 LCA

 3 */

 4 #include<stdio.h>

 5 #include<string.h>

 6 #include<stdlib.h>

 7 #include<algorithm>

 8 #include<iostream>

 9 #include<queue>

10 #include<map>

11 #include<math.h>

12 using namespace std;

13 typedef long long ll;

14 //typedef __int64 int64;

15 const int maxn = 10005;

16 const int inf = 0x7fffffff;

17 const double pi=acos(-1.0);

18 const double eps = 1e-8;

19 int deep[ maxn ],ace[ maxn ],fa[ maxn ];

20 //int dis[ maxn ];

21 struct node{

22     int u,next;

23 }edge[ maxn<<4 ];

24 int cnt,head[ maxn ];

25 void init(){

26     cnt = 0;

27     memset( fa,0,sizeof( fa ) );

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

29 }

30 void addedge( int a,int b){

31     edge[ cnt ].u = b;

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

33     head[ a ] = cnt++;

34 }

35 void dfs( int now,int now_father,int now_ace,int now_deep/*,int now_dis*/ ){

36     fa[ now ] = now_father;

37     ace[ now ] = now_ace;

38     deep[ now ] = now_deep;

39     //dis[ now ] = now_dis;

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

41         int v = edge[ i ].u;

42         //if( fa[v]==0 ){

43             dfs( v,now,now_ace,now_deep+1/*,now_dis+edge[ i ].val*/ );

44         //}

45     }

46 }

47 int find( int x,int y ){

48     if( x==y ) return x;

49     if( deep[x]>deep[y] ) return find( fa[x],y );

50     else return find( x,fa[y] );

51 }

52 int main(){

53     int ca;

54     scanf("%d",&ca);

55     while( ca-- ){

56         int n;

57         scanf("%d",&n);

58         int a,b;

59         init();

60         for( int i=0;i<n-1;i++ ){

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

62             addedge( a,b );

63         }

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

65         for( int i=1;i<=n;i++ ){

66             if( fa[i]==0 ){

67                 dfs( i,-1,i,0/*,0*/ );

68             }

69         }

70         /*

71         for( int i=1;i<=n;i++ ){

72             printf("fa[%d]=%d\n",i,fa[i]);

73         }

74         */

75         int father = find( a,b );

76         printf("%d\n",father);

77     }

78     return 0;

79 }

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