【POJ】1987 Distance Statistics 点分治

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传送门：【POJ】1987 Distance Statistics

题目分析：点分治入门题~

poj 1741 买一送一可不能错过~

代码如下：

#include <cstdio>#include <cstring>#include <algorithm>using namespace std ;typedef long long LL ;#define travel( e , H , u ) for ( Edge* e = H[u] ; e ; e = e -> next )#define rep( i , a , b ) for ( int i = ( a ) ; i <  ( b ) ; ++ i )#define rev( i , a , b ) for ( int i = ( a ) ; i >= ( b ) ; -- i )#define FOR( i , a , b ) for ( int i = ( a ) ; i <= ( b ) ; ++ i )#define clr( a , x ) memset ( a , x , sizeof a )#define cpy( a , x ) memcpy ( a , x , sizeof a )const int MAXN = 40005 ;const int MAXE = 80005 ;struct Edge {int v , c ;Edge* next ;} E[MAXE] , *H[MAXN] , *edge ;bool vis[MAXN] ;int siz[MAXN] ;int dep[MAXN] ;int num[MAXN] ;int tot_size ;int S[MAXN] ;int n , K ;int root ;int top ;int ans ;void clear () {ans = 0 ;root = 0 ;edge = E ;num[0] = n ;tot_size = n ;clr ( H , 0 ) ;clr ( vis , 0 ) ;}void addedge ( int u , int v , int c ) {edge -> v = v ;edge -> c = c ;edge -> next = H[u] ;H[u] = edge ++ ;}void get_root ( int u , int fa = 0 ) {siz[u] = 1 ;num[u] = 0 ;travel ( e , H , u ) {int v = e -> v ;if ( !vis[v] && v != fa ) {get_root ( v , u ) ;siz[u] += siz[v] ;num[u] = max ( num[u] , siz[v] ) ;}}num[u] = max ( num[u] , tot_size - siz[u] ) ;if ( num[u] < num[root] ) root = u ;}void get_dep ( int u , int fa = 0 ) {if ( dep[u] <= K ) S[top ++] = dep[u] ;siz[u] = 1 ;travel ( e , H , u ) {int v = e -> v ;if ( !vis[v] && v != fa ) {dep[v] = dep[u] + e -> c ;get_dep ( v , u ) ;siz[u] += siz[v] ;}}}int get_num ( int u , int len ) {top = 0 ;dep[u] = len ;get_dep ( u ) ;sort ( S , S + top ) ;int l = 0 , r = top - 1 , res = 0 ;while ( l < r ) {if ( S[l] + S[r] <= K ) {res += r - l ;++ l ;} else -- r ;}return res ;}void dfs ( int u ) {vis[u] = 1 ;ans += get_num ( u , 0 ) ;travel ( e , H , u ) {int v = e -> v ;if ( !vis[v] ) {ans -= get_num ( v , e -> c ) ;root = 0 ;get_root ( v ) ;tot_size = siz[v] ;dfs ( root ) ;}}}void solve () {int u , v , c ;clear () ;rep ( i , 1 , n ) {scanf ( "%d%d%d%*s" , &u , &v , &c ) ;addedge ( u , v , c ) ;addedge ( v , u , c ) ;}scanf ( "%d" , &K ) ;get_root ( 1 ) ;dfs ( root ) ;printf ( "%d\n" , ans ) ;}int main () {while ( ~scanf ( "%d%*d" , &n ) ) solve () ;return 0 ;}

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