【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。

  1 import java.lang.*;
  2 import java.io.*;
  3 import java.util.*;
  4 
  5 
  6 public class Main {
  7     
  8     public static void main(String[] args) throws java.lang.Exception {
  9         InputStream inputStream = System.in;
 10         OutputStream outputStream = System.out;
 11         InputReader in = new InputReader(inputStream);
 12         PrintWriter out = new PrintWriter(outputStream);
 13         TaskA solver = new TaskA();
 14         solver.solve(in, out);
 15         out.close();
 16     }
 17 }
 18 
 19 class TaskA {
 20     public final static int maxv = (int)(5e5+5);
 21     public final static int INF = 0x3f3f3f3f;
 22     int[] V = new int[maxv];
 23     int[] W = new int[maxv];
 24     int[] nxt = new int[maxv];
 25     int[] head = new int[maxv];
 26     int m, n, L, R;
 27     
 28     void init() {
 29         m = 0;
 30         Arrays.fill(head, -1);
 31     }
 32     
 33     void addEdge(int u, int v, int w) {
 34         V[m] = v;
 35         W[m] = w;
 36         nxt[m] = head[u];
 37         head[u] = m++;
 38     }
 39     
 40     public void solve(InputReader in, PrintWriter out) {
 41         int i;
 42         int u, v, w;
 43         int ans;
 44         
 45         while (true) {
 46             try {
 47                 n = in.nextInt();
 48             } catch (RuntimeException e) {
 49                 break;
 50             }
 51             L = in.nextInt();
 52             R = in.nextInt();
 53             init();
 54             for (i=1; i<n; ++i) {
 55                 u = in.nextInt();
 56                 v = in.nextInt();
 57                 w = in.nextInt();
 58                 addEdge(u, v, w);
 59             }
 60             ans = dfs(0, 0, 0);
 61             if (ans == INF)
 62                 out.println("Oh, my god!");
 63             else
 64                 out.println(ans);
 65         }
 66     }
 67     
 68     private int dfs(int u, int len, int now) {
 69         int ans = -1;
 70         
 71         if (head[u] == -1)
 72             return 0;
 73         int i, v, w;
 74         
 75         for (i=head[u]; i!=-1; i=nxt[i]) {
 76             v = V[i];
 77             w = W[i];
 78             int tmp = dfs(v, len+w, now^1) + w;
 79             if (tmp == INF)
 80                 continue;
 81             if (tmp>=L-len && tmp<=R-len) {
 82                 if (now == 0) {
 83                     if (ans==-1 || tmp>ans)
 84                         ans = tmp;
 85                 } else {
 86                     if (ans==-1 || tmp<ans)
 87                         ans = tmp;
 88                 }
 89             }
 90         }
 91         
 92         if (ans == -1)
 93             return INF;
 94         return ans;
 95     }
 96 }
 97 
 98 class InputReader {
 99     public BufferedReader reader;
100     public StringTokenizer tokenizer;
101     
102     public InputReader(InputStream stream) {
103         reader = new BufferedReader(new InputStreamReader(stream), 32768);
104         tokenizer = null;
105     }
106     
107     public String next() {
108         while (tokenizer==null || !tokenizer.hasMoreTokens()) {
109             try {
110                 tokenizer = new StringTokenizer(reader.readLine());
111             } catch (IOException e) {
112                 throw new RuntimeException(e);
113             }
114         }
115         return tokenizer.nextToken();
116     }
117     
118     public int nextInt() {
119         return Integer.parseInt(next());
120     }
121 }

 

posted on 2015-12-31 00:03  Bombe  阅读(144)  评论(0)  编辑  收藏  举报

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