终于自己独立A了一道点分治。
点分治的题目和树规的题目很像，都是在树上乱搞，但点分治一般和路径更相关，如果用树规做会感觉冗余状态太多，内存和时间都无法承受，如果不用动态规划，直接在原树上运用这道题的方法，又无法保证时间复杂度（点分治让我们的算法对原树的形态依赖更小，可以保证时间复杂度）。
1 /************************************************************** 2 Problem: 3697 3 User: idy002 4 Language: C++ 5 Result: Accepted 6 Time:2480 ms 7 Memory:14012 kb 8 ****************************************************************/ 9 10 #include <cstdio> 11 #define N 100010 12 #define fprintf(...) 13 14 int n; 15 int head[N], dest[N+N], wght[N+N], next[N+N], ntot; 16 int fat[N], vis[N], siz[N], bac[N], dis[N], cur_root, cur_siz; 17 int vv[N+N], svv[N+N][2], cvv[N+N][2]; 18 int stkc[N+N], tpc, stks[N+N], tps; 19 long long ans; 20 21 void insert( int u, int v, int w ) { 22 ntot++; 23 next[ntot] = head[u]; 24 wght[ntot] = w ? 1 : -1; 25 dest[ntot] = v; 26 head[u] = ntot; 27 } 28 void dfs_root( int u ) { 29 siz[u] = 1, bac[u] = 0; 30 for( int t=head[u]; t; t=next[t] ) { 31 int v=dest[t]; 32 if( vis[v] || v==fat[u] ) continue; 33 fat[v] = u; 34 dfs_root(v); 35 siz[u] += siz[v]; 36 if( siz[v]>bac[u] ) bac[u]=siz[v]; 37 } 38 if( cur_siz-siz[u]>bac[u] ) bac[u]=cur_siz-siz[u]; 39 if( bac[u]<bac[cur_root] ) cur_root=u; 40 } 41 void dfs_dis( int u ) { 42 if( dis[u]==0 && vv[N+0]>1 ) 43 ans++; 44 bool ok = vv[N+dis[u]]; 45 if( ok ) { 46 ans += svv[N-dis[u]][0]+svv[N-dis[u]][1]; 47 cvv[N+dis[u]][1]++; 48 } else { 49 ans += svv[N-dis[u]][1]; 50 cvv[N+dis[u]][0]++; 51 } 52 stkc[++tpc] = dis[u]; 53 fprintf( stderr, "Arrived %d cur_ans = %lld ", u, ans ); 54 vv[N+dis[u]]++; 55 for( int t=head[u]; t; t=next[t] ) { 56 int v=dest[t], w=wght[t]; 57 if( vis[v] || v==fat[u] ) continue; 58 dis[v] = dis[u]+w; 59 fat[v] = u; 60 dfs_dis( v ); 61 } 62 vv[N+dis[u]]--; 63 } 64 void build_vdcp( int rt ) { 65 /* found the core */ 66 cur_siz = siz[rt]; 67 cur_root = 0; 68 fat[rt] = rt; 69 dfs_root( rt ); 70 /* collect the info */ 71 rt = cur_root; 72 vis[rt] = true; 73 fprintf( stderr, "cur_root = %d ", rt ); 74 for( int t=head[rt]; t; t=next[t] ) { 75 int u=dest[t], w=wght[t]; 76 if( vis[u] ) continue; 77 tpc = 0; 78 vv[N+0]++; 79 fat[u] = rt; 80 dis[u] = w; 81 dfs_dis( u ); 82 vv[N+0]--; 83 while( tpc ) { 84 int v = stkc[tpc--]; 85 if( !cvv[N+v][0] && !cvv[N+v][1] ) continue; 86 svv[N+v][0] += cvv[N+v][0]; 87 svv[N+v][1] += cvv[N+v][1]; 88 stks[++tps] = v; 89 cvv[N+v][0] = cvv[N+v][1] = 0; 90 } 91 } 92 while( tps ) { 93 int v = stks[tps--]; 94 svv[N+v][0] = svv[N+v][1] = 0; 95 } 96 for( int t=head[rt]; t; t=next[t] ) { 97 int u=dest[t]; 98 if( vis[u] ) continue; 99 build_vdcp( u ); 100 } 101 } 102 int main() { 103 scanf( "%d", &n ); 104 for( int i=1,u,v,w; i<n; i++ ) { 105 scanf( "%d%d%d", &u, &v, &w ); 106 insert( u, v, w ); 107 insert( v, u, w ); 108 } 109 bac[0] = n; 110 siz[1] = n; 111 build_vdcp(1); 112 printf( "%lld ", ans ); 113 }