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
     
      =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