挑战程序竞赛系列（59）：4.6树上的分治法（2）

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201709/P1741.txt";

    public static void main(String[] args) throws IOException {
        new Main().run();
    }

    static final int MAX_N = 10000 + 16;
    static final int INF   = 0x3f3f3f3f;

    class Edge{
        int to;
        int cost;
        int next;
        Edge(int to, int cost, int next){
            this.to = to;
            this.cost = cost;
            this.next = next;
        }

        @Override
        public String toString() {
            return to + " " + cost + " " + next;
        }

    }

    Edge[] edges = new Edge[MAX_N << 1];
    int N, K, tot, cenv, minv, ans, point;
    int[] head, son;
    int[] dis;

    boolean[] visited;

    void init() {
        head = new int[MAX_N];
        son  = new int[MAX_N];
        dis  = new int[MAX_N];
        visited = new boolean[MAX_N];
        cenv = point = tot = 0;
        minv = INF;
        Arrays.fill(head,  -1);
    }

    void add(int from, int to, int cost) {
        edges[tot] = new Edge(to, cost, head[from]);
        head[from] = tot++;
    }

    void dfs(int u, int fa) {
        son[u] = 0;
        int maxv = 0;
        for (int i = head[u]; i != -1; i = edges[i].next) {
            int v = edges[i].to;
            if (v == fa || visited[v]) continue;
            dfs(v, u);
            son[u] += son[v] + 1;
            maxv = Math.max(maxv, son[v] + 1);
        }

        maxv = Math.max(maxv, point - 1 - son[u]);
        if (maxv < minv) {
            minv = maxv;
            cenv = u;
        }
    }

    void getDis(int u, int fa, int dist) {
        dis[tot++] = dist;
        for (int i = head[u]; i != -1; i = edges[i].next) {
            int v = edges[i].to;
            if (v == fa || visited[v]) continue;
            getDis(v, u, dist + edges[i].cost);
        }
    }

    int count(int u, int d) {
        tot = 0;
        getDis(u, -1, d);
        Arrays.sort(dis, 0, tot);
        int l = 0, r = tot - 1, res = 0;
        while (l < r) {
            if (dis[l] + dis[r] <= K) {
                res += r - l;
                l ++;
            }
            else r --;
        }
        return res;
    }

    void solve(int u) {
        minv = INF;
        point = point != 0 ? son[u] + 1 : N;
        dfs(u, -1);
        int root = cenv;
        visited[root] = true;
        ans += count(root, 0);
        for (int i = head[root]; i != -1; i = edges[i].next) {
            int v = edges[i].to;
            if (visited[v]) continue;
            ans -= count(v, edges[i].cost);
            solve(v);
        }
    }


    void read() {
        while (true) {
            N = ni();
            K = ni();
            if (N == 0 && K == 0) break;

            init();
            for (int i = 1; i < N; ++i) {
                int from = ni();
                int to   = ni();
                int cost = ni();
                add(from, to, cost);
                add(to, from, cost);
            }

            ans = 0;
            solve(1);
            out.println(ans);
        }
    }

    FastScanner in;
    PrintWriter out;

    void run() throws IOException {
        boolean oj;
        try {
            oj = ! System.getProperty("user.dir").equals("F:\\java_workspace\\leetcode");
        } catch (Exception e) {
            oj = System.getProperty("ONLINE_JUDGE") != null;
        }

        InputStream is = oj ? System.in : new FileInputStream(new File(INPUT));
        in = new FastScanner(is);
        out = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        read();
        out.flush();
        if (!oj){
            System.out.println("[" + (System.currentTimeMillis() - s) + "ms]");
        }
    }

    public boolean more(){
        return in.hasNext();
    }

    public int ni(){
        return in.nextInt();
    }

    public long nl(){
        return in.nextLong();
    }

    public double nd(){
        return in.nextDouble();
    }

    public String ns(){
        return in.nextString();
    }

    public char nc(){
        return in.nextChar();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;
        boolean hasNext;

        public FastScanner(InputStream is) throws IOException {
            br = new BufferedReader(new InputStreamReader(is));
            hasNext = true;
        }

        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (Exception e) {
                    hasNext = false;
                    return "##";
                }
            }
            return st.nextToken();
        }

        String next = null;
        public boolean hasNext(){
            next = nextToken();
            return hasNext;
        }

        public int nextInt() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Integer.parseInt(more);
        }

        public long nextLong() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Long.parseLong(more);
        }

        public double nextDouble() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Double.parseDouble(more);
        }

        public String nextString(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more;
        }

        public char nextChar(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more.charAt(0);
        }
    }

    static class ArrayUtils {

        public static void fill(int[][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                Arrays.fill(f[i], value);
            }
        }

        public static void fill(int[][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }

        public static void fill(int[][][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }
    }
}