Developing Algorithms Using Strings Practice

Sample questions

5 of 19 — sign in to practice the rest with adaptive difficulty and mastery tracking.

1. Sample 1difficulty 2/5

   for (String s : list) {
       System.out.println(s);
   }

   Which traditional loop is equivalent for an ArrayList<String> list?

   • A

     for (int i = 0; i < list.size(); i++) System.out.println(list[i]);

   • B

     for (int i = 0; i < list.size(); i++) System.out.println(list.get(i));

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   • C

     for (int i = 0; i < list.length; i++) System.out.println(list.get(i));

   • D

     for (int i = 1; i <= list.size(); i++) System.out.println(list.get(i));

   Why

   ArrayList exposes size() and get(i); the indexed loop must use both for the same elements in order.

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2. Sample 2difficulty 2/5

   String s = "hello";
   String r = "";
   for (int i = s.length() - 1; i >= 0; i--) {
     r += s.charAt(i);
   }

   What is r?

   • A

     hellohello

   • B

     olleh

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   • C

     hello

   • D

     (empty)

   Why

   The loop appends chars in reverse, producing "olleh".

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3. Sample 3difficulty 2/5

   String s = "Java";
   StringBuilder sb = new StringBuilder(s);
   String r = sb.reverse().toString();

   What is r?

   • A

     JAVa

   • B

     avaJ

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   • C

     ajva

   • D

     Java

   Why

   StringBuilder.reverse() reverses the character order.

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4. Sample 4difficulty 2/5

   public static boolean isAna(String a, String b) {
     if (a.length() != b.length()) return false;
     char[] ca = a.toCharArray();
     char[] cb = b.toCharArray();
     java.util.Arrays.sort(ca);
     java.util.Arrays.sort(cb);
     return java.util.Arrays.equals(ca, cb);
   }
   // call: isAna("ab", "abc")

   What does it return?

   • A

     null

   • B

     false

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   • C

     true

   • D

     compile error

   Why

   Different lengths can't be anagrams; returns false immediately.

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5. Sample 5difficulty 3/5

   public static boolean isPal(String s) {
     int i = 0, j = s.length() - 1;
     while (i < j) {
       if (s.charAt(i) != s.charAt(j)) return false;
       i++; j--;
     }
     return true;
   }
   // call: isPal("hello")

   What does isPal("hello") return?

   • A

     0

   • B

     exception

   • C

     true

   • D

     false

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   Why

   'h' != 'o', so the function returns false.

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