LibieOJ 6170 字母树 （Trie）

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)
#define dec(i, a, b)	for (int i(a); i >= (b); --i)

typedef long long LL;

const int N = 5010;

struct node{
	int son[26];
	int cnt, tot;
	int sum[27];
} trie[N];

int n, m, q;

vector <int> v[N];
vector <char> ch[N];

int ans[N][N];

void build_trie(int x, int fa, int p){
	++trie[p].cnt;
	int i = -1;
	for (auto u : v[x]){
		++i;
		if (u == fa) continue;
		int c = ch[x][i] - ‘a‘;
		if (trie[p].son[c] == 0){
			++m;
			trie[p].son[c] = m;
		}

		build_trie(u, x, trie[p].son[c]);
	}
}

void get_answer(int x, int fa, int p, int cnt, int ans[]){
	ans[x] = cnt;
	cnt += trie[p].cnt;
	int i = -1;
	for (auto u : v[x]){
		++i;
		if (u == fa) continue;
		int c = ch[x][i] - ‘a‘;
		get_answer(u, x, trie[p].son[c], cnt + trie[p].sum[c], ans);
	}
}

int main(){

	scanf("%d%d", &n, &q);
	rep(i, 1, n - 1){
		int x, y;
		char z[10];
		scanf("%d%d%s", &x, &y, z);
		v[x].push_back(y);
		v[y].push_back(x);
		ch[x].push_back(z[0]);
		ch[y].push_back(z[0]);
	}

	rep(i, 1, n){
		m = 0;
		memset(trie, 0, sizeof trie);
		build_trie(i, 0, 0);
		dec(j, m, 0){
			trie[j].tot = trie[j].cnt;
			rep(k, 0, 25){
				trie[j].sum[k + 1] = trie[j].sum[k];
				if (trie[j].son[k] > 0){
					trie[j].tot += trie[trie[j].son[k]].tot;
					trie[j].sum[k + 1] += trie[trie[j].son[k]].tot;
				}
			}

			rep(k, 1, 25){
				trie[trie[j].son[k - 1]].cnt;
			}

		}

		get_answer(i, 0, 0, 0, ans[i]);
	}

	while (q--){
		int x, y;
		scanf("%d%d", &x, &y);
		printf("%d\n", ans[x][y] - 1);
	}

	return 0;
}