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  1. import java.io.StringReader;
  2. import java.util.ArrayDeque;
  3. import java.util.Deque;
  4. import java.util.Optional;
  5. import java.util.Scanner;
  6. import java.util.Spliterator;
  7. import java.util.Spliterators;
  8. import java.util.stream.Collectors;
  9. import java.util.stream.Stream;
  10. import java.util.stream.StreamSupport;
  11.  
  12. class Stacker {
  13.  
  14. 	private final Deque<Integer> stack = new ArrayDeque<>();
  15.  
  16. 	public Optional<Integer> processOperation(String op) {
  17. 		char opc = op.charAt(0);
  18. 		switch(opc) {
  19. 		case '1':
  20. 			int previous = stack.isEmpty() ? Integer.MIN_VALUE : stack.peek();
  21. 			int max = Math.max(previous, Integer.parseInt(op.substring(1).trim()));
  22. 			stack.push(max);
  23. 			return Optional.empty();
  24. 		case '2':
  25. 			if (stack.isEmpty()) {
  26. 				throw new IllegalStateException("Cannot pop empty stack");
  27. 			}
  28. 			stack.pop();
  29. 			return Optional.empty();
  30. 		case '3':
  31. 			if (stack.isEmpty()) {
  32. 				throw new IllegalStateException("Cannot max empty stack");
  33. 			}
  34. 			return Optional.of(stack.peek());
  35. 		default:
  36. 			throw new IllegalStateException("Unknown operation:" + op);
  37. 		}
  38. 	}
  39.  
  40.  
  41.  
  42. 	public static void main(String[] args) {
  43. 		String testdata = "10\n" + 
  44. 				"1 97\n" + 
  45. 				"2\n" + 
  46. 				"1 20\n" + 
  47. 				"2\n" + 
  48. 				"1 26\n" + 
  49. 				"1 20\n" + 
  50. 				"2\n" + 
  51. 				"3\n" + 
  52. 				"1 91\n" + 
  53. 				"3";
  54.  
  55. 		try (Scanner scanner = new Scanner(new StringReader(testdata))) {
  56. 			scanner.useDelimiter("\\s*\\n");
  57. 			int count = Integer.parseInt(scanner.next());
  58. 			// convert STDIN lines to a stream
  59. 			Stream<String> commands = StreamSupport.stream(Spliterators.spliterator(scanner, count, Spliterator.ORDERED), false);
  60. 			// process the operations:
  61. 			Stacker stacker = new Stacker();
  62. 			String report = commands.map(stacker::processOperation)
  63. 					.filter(Optional::isPresent)
  64. 					.map(opt -> String.valueOf(opt.get()))
  65. 					.collect(Collectors.joining("\n"));
  66. 			System.out.println(report);
  67. 		}
  68. 	}
  69.  
  70. }
  71.  
Success #stdin #stdout 0.14s 4386816KB
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https://ideone.com/1jREos
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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