I

状压搜索加剪枝。

#include <iostream>#include <stdio.h>#include <cstring>#include <algorithm>#include <cmath>#include <vector>using namespace std;const int N = 10009;struct node{ int v, l;node() {};node(int _v, int _l):v(_v),l(_l) {};};vector<node>Tree[N];int n, k, size, s[N], f[N], root, deep[N], ans;vector<int>dep;bool used[N];int x, y, z;void get_root(int now, int fa){s[now] = 1;f[now] = 0;for (int i = 0; i < Tree[now].size(); i++) {int u = Tree[now][i].v;if (u != fa && !used[u]) {get_root(u, now);s[now] += s[u];f[now] = max(f[now], s[u]);}}f[now] = max(f[now], size - s[now]);if (f[now] < f[root]) root = now;}void get_dep(int now, int fa) {dep.push_back(deep[now]);for (int i = 0; i < Tree[now].size(); i++) {int u = Tree[now][i].v;if (u !=  fa && ! used[u]) {deep[u] = deep[now] + Tree[now][i].l;get_dep(u, now);}}}int calc(int now, int init){dep.clear();deep[now] = init;get_dep(now, 0);sort(dep.begin(), dep.end());int ret = 0;for (int l = 0, r = dep.size()-1; l < r;) {if (dep[l] + dep[r] <= k) ret += r-l++;else r--;}return ret;}void work(int now) {ans += calc(now, 0);used[now] =true;for (int i = 0; i < Tree[now].size(); i++) {int u = Tree[now][i].v;if (!used[u]) {ans -= calc(u, Tree[now][i].l);f[0] = size = s[u];get_root(u, root = 0);work(root);}}}int main(){while (scanf("%d%d", &n, &k) != EOF) {if (n == 0 && k == 0) break;memset(used, 0, sizeof(used));for (int i = 1; i <= n; i++) Tree[i].clear();for (int i = 1; i < n; i++) {scanf("%d%d%d", &x, &y, &z);Tree[x].push_back(node(y, z));Tree[y].push_back(node(x, z));}f[0] = size = n;get_root(1, root = 0);ans = 0;work(root);printf("%d\n", ans);  }return 0;}