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  1. import java.util.ArrayList;
  2. import java.util.List;
  3.  
  4. public class Main implements Runnable {
  5.     public static void main(String[] args) {
  6.         new Thread(null, new Main(), "", 256 * (1L << 20)).start();
  7.     }
  8.  
  9.     @Override
  10.     public void run() {
  11.         int n = 500000;
  12.         List<Integer>[] g = new List[n];
  13.         for (int i = 0; i < n; i++) {
  14.             g[i] = new ArrayList<>();
  15.         }
  16.         for (int i = 1; i < n; i++) {
  17.             int p = i - 1;
  18.             g[i].add(p);
  19.             g[p].add(i);
  20.         }
  21.  
  22.         long t1 = System.nanoTime();
  23.         for (int i = 0; i < 100000; i++) {
  24.             dfs(0, -1, g, 0, 0); // JIT please
  25.         }
  26.         int result = dfs(0, -1, g, 0, Integer.MAX_VALUE);
  27.         long t2 = System.nanoTime();
  28.         System.out.println("time = " + (t2 - t1) / 1.0e9 + " sec, result = " + result);
  29.     }
  30.  
  31.     private int dfs(int x, int p, List<Integer>[] g, int curDepth, int maxDepth) {
  32.         if (curDepth > maxDepth) {
  33.             return 0;
  34.         }
  35.         int result = 1;
  36.         for (int y : g[x]) {
  37.             if (y == p) {
  38.                 continue;
  39.             }
  40.             result += dfs(y, x, g, curDepth + 1, maxDepth);
  41.         }
  42.         return result;
  43.     }
  44. }
Success #stdin #stdout 0.24s 153552KB
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time = 0.049763821 sec, result = 500000
https://ideone.com/EG2opW
with warming up, java 8
language:
Java (12.0.1)
created:
3 years ago
visibility:
secret

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