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  1. import java.lang.reflect.Field;
  2.  
  3. public class Main {
  4.  
  5.     public static void main(String[] args) {
  6.         test("foo", "foo", true);
  7.         test("foo", "foobar", true);
  8.         test("oob", "foobar", true);
  9.         test("oobar", "foobar", true);
  10.         test("barbar", "foobar", false);
  11.         test("blip", "foo", false);
  12.         test("", "troll", true);
  13.         test("foo", "", false);
  14.         test("test", "testing", true);
  15.         test("dog", "cat", false);
  16.         test("test", "Testing", false);
  17.     }
  18.  
  19.     private static void test(String needle, String haystack, boolean expected) {
  20.         boolean isSubstring = isSubstring(needle, haystack);
  21.         if (isSubstring != expected) {
  22.             System.out.println("You're fired!");
  23.         }
  24.         System.out.printf("\"%s\" contained in \"%s\"? %b expected: %b%n", needle, haystack, isSubstring, expected);
  25.     }
  26.  
  27.     public static boolean isSubstring(String needle, String haystack) {
  28.  
  29.         if (haystack.length() < needle.length()) {
  30.             return false;
  31.         }
  32.  
  33.         char[] needleChars = getCharArray(needle);
  34.         char[] haystackChars = getCharArray(haystack);
  35.         for (int i = 0; i < haystack.length(); i++) {
  36.             if (isSubstringAtPosition(needleChars, haystackChars, i)) {
  37.                 return true;
  38.             }
  39.         }
  40.         return false;
  41.  
  42.     }
  43.  
  44.     private static boolean isSubstringAtPosition(char[] needle, char[] haystack, int haystackPosition) {
  45.         if (needle.length > (haystack.length - haystackPosition)) {
  46.             return false;
  47.         }
  48.         for (char c : needle) {
  49.             if (haystack[haystackPosition++] != c) {
  50.                 return false;
  51.             }
  52.         }
  53.         return true;
  54.     }
  55.  
  56.     public static char[] getCharArray(String string) {
  57.         Field value;
  58.         try {
  59.             value = String.class.getDeclaredField("value");
  60.             value.setAccessible(true);
  61.             return (char[]) value.get(string);
  62.         } catch (SecurityException e) {
  63.             e.printStackTrace();
  64.         } catch (NoSuchFieldException e) {
  65.             e.printStackTrace();
  66.         } catch (IllegalArgumentException e) {
  67.             e.printStackTrace();
  68.         } catch (IllegalAccessException e) {
  69.             e.printStackTrace();
  70.         }
  71.         throw new RuntimeException("oops");
  72.     }
  73. }
  74.  
Success #stdin #stdout 0.08s 380160KB
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Standard input is empty
stdout
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"foo" contained in "foo"? true expected: true
"foo" contained in "foobar"? true expected: true
"oob" contained in "foobar"? true expected: true
"oobar" contained in "foobar"? true expected: true
"barbar" contained in "foobar"? false expected: false
"blip" contained in "foo"? false expected: false
"" contained in "troll"? true expected: true
"foo" contained in ""? false expected: false
"test" contained in "testing"? true expected: true
"dog" contained in "cat"? false expected: false
"test" contained in "Testing"? false expected: false
https://ideone.com/JWcsgX
language:
Java (HotSpot 12)
created:
12 years ago
visibility:
public

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