【HDOJ】3660 Alice and Bob's Trip

就是一个基本的dfs。可关键问题是c/c++/g++光输入就超时了。还是写java过的，毕竟时限4s。都放弃希望了，没想到还真过了。

 import java.lang.*;
 import java.io.*;
 import java.util.*;

 public class Main {

     public static void main(String[] args) throws java.lang.Exception {
         InputStream inputStream = System.in;
         OutputStream outputStream = System.out;
         InputReader in = new InputReader(inputStream);
         PrintWriter out = new PrintWriter(outputStream);
         TaskA solver = new TaskA();
         solver.solve(in, out);
         out.close();
     }
 }

 class TaskA {
     public final static int maxv = (int)(5e5+5);
     public final static int INF = 0x3f3f3f3f;
     int[] V = new int[maxv];
     int[] W = new int[maxv];
     int[] nxt = new int[maxv];
     int[] head = new int[maxv];
     int m, n, L, R;

     void init() {
         m = 0;
         Arrays.fill(head, -1);
     }

     void addEdge(int u, int v, int w) {
         V[m] = v;
         W[m] = w;
         nxt[m] = head[u];
         head[u] = m++;
     }

     public void solve(InputReader in, PrintWriter out) {
         int i;
         int u, v, w;
         int ans;

         while (true) {
             try {
                 n = in.nextInt();
             } catch (RuntimeException e) {
                 break;
             }
             L = in.nextInt();
             R = in.nextInt();
             init();
             for (i=1; i<n; ++i) {
                 u = in.nextInt();
                 v = in.nextInt();
                 w = in.nextInt();
                 addEdge(u, v, w);
             }
             ans = dfs(0, 0, 0);
             if (ans == INF)
                 out.println("Oh, my god!");
             else
                 out.println(ans);
         }
     }

     private int dfs(int u, int len, int now) {
         int ans = -1;

         if (head[u] == -1)
             return 0;
         int i, v, w;

         for (i=head[u]; i!=-1; i=nxt[i]) {
             v = V[i];
             w = W[i];
             int tmp = dfs(v, len+w, now^1) + w;
             if (tmp == INF)
                 continue;
             if (tmp>=L-len && tmp<=R-len) {
                 if (now == 0) {
                     if (ans==-1 || tmp>ans)
                         ans = tmp;
                 } else {
                     if (ans==-1 || tmp<ans)
                         ans = tmp;
                 }
             }
         }

         if (ans == -1)
             return INF;
         return ans;
     }
 }

 class InputReader {
     public BufferedReader reader;
     public StringTokenizer tokenizer;

     public InputReader(InputStream stream) {
         reader = new BufferedReader(new InputStreamReader(stream), 32768);
         tokenizer = null;
     }

     public String next() {
         while (tokenizer==null || !tokenizer.hasMoreTokens()) {
             try {
                 tokenizer = new StringTokenizer(reader.readLine());
             } catch (IOException e) {
                 throw new RuntimeException(e);
             }
         }
         return tokenizer.nextToken();
     }

     public int nextInt() {
         return Integer.parseInt(next());
     }
 }