/* NetIds: djg17, mdg39. Time spent: hh hours, mm minutes. */
/** A collection of static String utility functions.
* All methods assume that String parameters are non-null.
*
* If any method is called with arguments that do not satisfy the preconditions,
* the behavior is undefined (it can do anything you want). For example, you
* could (but do not have to) use assert statements to test preconditions.
*/
public class A2 {
/* Implementation notes:
*
* Wherever possible, prefer library functions to writing your own loops.
*
* The more complicated your loops become, the more important it is to explain
* the logic in comments. We don't explain break and continue. We prefer that
* you don't use them.
*
* When writing comments within a method body, you may find it useful to
* use multi-line comments to describe WHAT the code doing, and single-line
* comments to describe HOW it is doing it. For example:
*
* /* Remove the unfrobnicatable whizbangs * /
* for (...)
* // NOTE: a whizbang is frobnicatable if it has two or more tails
* ...
*
* /* Frobnicate all the remaining whizbangs * /
* for (...)
* ...
*/
/* Notes on Java if statements and loops:
*
* Write an if statement like this:
*
* if (boolean-expression) {
* do this if boolean-expression is true
* }
*
* Write an if-else statement like this:
*
* if (boolean-expression) {
* do this if boolean-expression is true
* } else {
* do this if boolean-expression is false
* }
*
* Write a while-loop like this:
*
* while ( boolean-expression ) {
* repetend (the loop body, "the thing to be repeated")
* }
*
* To execute the while-loop, do the following:
*
* 1. Evaluate the boolean-expression; if is is false, stop.
* 2. Execute the repetend.
* 3. Continue again at step 1.
*
* Write a for-loop to do-something several times, with i having values in
* m..n-1 (i.e. with i being m, m+1, m+2, ..., n-1).
*
* for (int i= m; i < n; i= i+1) {
* repetend
* }
*
* The for-loop above is equivalent to the while-loop below, except that
* local variable i is NOT usable after the loop; its scope is its assignment
* together with the loop.
*
* int i= m;
* while (i < n) {
* repetend
* i= i+1;
* }
*/
/** Return either s1 + s2 or s1 - s2, depending on b.
* If b is true, return the sum, otherwise return the difference.
*/
public static int sumDif(boolean b, int s1, int s2) {
// This method is already implemented; it is here to give you something
// to test, and to show you different ways of writing return statements.
if (b) {
int s;
s = s1 + s2;
return s;
// equivalently:
// int s = s1 + s2;
// return s;
// or simply: return s1 + s2;
}
// b is false;
return s1 - s2;
}
/** Return true iff the first half of s is the same as the second half of s.
* Examples: For s = "" return true
* For s = "xxx" return false (if the length is odd, it's false)
* For s = "xxxx" return true
* For s = "hellohello" return true
* For s = "helloworld" return false
*/
public static boolean isDoubled(String s) {
// TODO: There is no need for a loop. Do not use a loop.
// Be sure to use s1.equals(s2) to test for equality of strings s1 and s2.
// Do not use s1 == s2.
return false;
}
/** Return s with its characters reversed.
* Examples: if s = "" return ""
* if s = "b" return "b"
* if s = "abc", return "cba"
* if s = "xxx", return "xxx"
*/
public static String reverse(String s) {
// TODO:
return "";
}
/** Return s but with each occurrence of a character in input replaced
* by the corresponding character in output.
* A character that does not appear in input is unchanged.
*
* Precondition: input and output are the same length.
* No character in input appears in output (otherwise,
* the idea of replacement might be ambiguous, depending
* on the order in which replacemens are done).
*
* Examples: encode("hello world", "", "") = "hello world"
* encode("hello world", "abc", "lmn") = "hello world"
* encode("hello world", "hod", "xyz") = "xelly wyrlz"
* encode("hello world", "helowrd", ".......") = "..... ....."
*/
public static String encode(String s, String input, String output) {
// TODO This needs only ONE for-loop with a single statement in the loop
// body. Look for a suitable String method!
return "";
}
/** Return the shortest substring x of s such that s = x + x + ⋯ + x.
* Examples: For s = "" return ""
* For s = "xxxxxxxxx" return "x"
* For s = "xyxyxyxy" return "xy"
* For s = "hellohellohello" return "hello"
* For s = "hellohelloworld" return "hellohelloworld"
* For s = "hellohel" return "hellohel"
*/
public static String deduplicate(String s) {
//TODO This, no doubt, requires nested loops
return "";
}
/** Interpret a string as a formula and evaluate it.
*
* Formulas consist of a series of numbers separated by the
* operators '+' or '-'. Formulas may contain space characters
* between the numbers and the operators.
*
* Precondition: s is a valid formula and contain at least one number
*
* Examples: evaluate("3") returns 3
* evaluate("3 + 4") returns 7
* evaluate("100 - 25+50") returns 125
* evaluate("9") returns 9
* evaluate(" 7 + 7 + 7 ") returns 21
*/
public static int evaluate(String s) {
// TODO You can use Integer.parseInt to convert a string
// (like "12345") to the corresponding integer (12345).
return 0;
}
}