HDU3794+字典树

字典树;

这里字典树用于存储dis这些数。。。然后对于某个数x来说，要使得它变大，就要找到一个与它能“合适”与它异或的数。

View Code

  1 /*

  2 字典树+异或

  3 a^b = (a^c)^(b^c)

  4 */

  5 #include<stdio.h>

  6 #include<string.h>

  7 #include<stdlib.h>

  8 const int maxn = 100005;

  9 const int maxm = 31;

 10 int tree[ maxn*maxm ][ 2 ];

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

 12 struct node{

 13     int u,next,val;

 14 };

 15 node edge[ maxn<<2 ];

 16 int cnt,head[ maxn ];

 17 int tree_index;

 18 

 19 void init(){

 20     memset( dis,0,sizeof( dis ));

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

 22     cnt = 0;

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

 24     memset( tree,-1,sizeof( tree ) );

 25 }

 26 

 27 void addedge( int a,int b,int c ){

 28     edge[ cnt ].u = b;

 29     edge[ cnt ].val = c;

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

 31     head[ a ] = cnt++;

 32 }

 33 

 34 void dfs( int now ){

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

 36         int u = edge[ i ].u;

 37         if( vis[ u ] == 0 ){

 38             vis[ u ] = 1;

 39             dis[ u ] = dis[ now ]^edge[ i ].val;

 40             dfs( u );

 41         }

 42     }

 43     return ;

 44 }//求出其他点到根的异或值

 45 

 46 int find_the_max( int aim ){

 47     int res = 0;

 48     int id = 0;

 49     for( int i=30;i>=0;i-- ){

 50         int one_bit = (aim>>i)&1;

 51         if( one_bit==0 ){

 52             if( tree[ id ][ 1 ]!=-1 ){

 53                 res += 1<<i;

 54                 id = tree[ id ][ 1 ];

 55             }

 56             else if( tree[ id ][ 0 ]!=-1 ) id = tree[ id ][ 0 ];

 57             else break;

 58         }

 59         else if( one_bit==1 ){

 60             if( tree[ id ][ 0 ]!=-1 ){

 61                 res += 1<<i;

 62                 id = tree[ id ][ 0 ];

 63             }

 64             else if( tree[ id ][ 1 ]!=-1 ) id = tree[ id ][ 1 ];

 65             else break;

 66         }

 67     }

 68     return res;

 69 }/*贪心，对于当前一个数x，异或某个数y之后变大，必须求一个数从高位到低位和x不同的。。*/

 70 

 71 void rebuild_tree( int aim ){

 72     int id = 0;

 73     for( int i=30;i>=0;i-- ){

 74         int one_bit = (aim>>i)&1;

 75         if( tree[ id ][ one_bit ]==-1 ){

 76             tree[ id ][ one_bit ] = tree_index++;

 77         }

 78         id = tree[ id ][ one_bit ];

 79     }

 80     return ;

 81 }//把dis[]变为2进制，存入字典数（从当前的tree_index开始存储）        

 82 

 83 void solve( int n ){

 84     int ans = 0;

 85     tree_index = 1;

 86     for( int i=0;i<n;i++ ){

 87         int tmp_ans = find_the_max( dis[ i ] );

 88         if( tmp_ans>ans ) ans = tmp_ans;

 89         rebuild_tree( dis[i] );

 90     }

 91     printf("%d\n",ans);

 92     return ;

 93 }

 94 

 95 int main(){

 96     int n;

 97     while( scanf("%d",&n)!=EOF ){

 98         int a,b,c;

 99         init();

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

101             scanf("%d%d%d",&a,&b,&c);

102             addedge( a,b,c );

103             addedge( b,a,c );

104         }

105         

106         vis[ 0 ] = 1;

107         dfs( 0 );

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

109         //    printf("dis[%d]=%d\n",i,dis[i]);

110         solve( n );

111         

112     }

113     return 0;

114 }