CMU 15-112 Fall 2015 Homework 3 Practice
(Due never)

sameChars(s1, s2)
Write the function sameChars(s1, s2) that takes two strings and returns True if the two strings are composed of the same characters (though perhaps in different numbers and in different orders) -- that is, if every character that is in the first string, is in the second, and vice versa -- and False otherwise. This test is case-sensitive, so "ABC" and "abc" do not contain the same characters. The function returns False if either parameter is not a string, but returns True if both strings are empty (why?).

wordWrap(text, width)
Write the function wordWrap(text, width) that takes a string of text (containing only lowercase letters or spaces) and a positive integer width, and returns a possibly-multiline string that matches the original string, only with line wrapping at the given width. So wordWrap("abc", 3) just returns "abc", but wordWrap("abc",2) returns a 2-line string, with "ab" on the first line and "c" on the second line. After you complete word wrapping in this way, only then: All spaces at the start and end of each resulting line should be removed, and then all remaining spaces should be converted to dashes ("-"), so they can be easily seen in the resulting string. Here are some test cases for you:
```
        assert(wordWrap("abcdefghij", 4)  ==  """\
abcd
efgh
ij""")
        assert(wordWrap("a b c de fg",  4)  ==  """\
a-b
c-de
fg""")
```

largestNumber(text)
largestNumber: Write the function largestNumber(text) that takes a string of text and returns the largest int value that occurs within that text, or None if no such value occurs. You may assume that the only numbers in the text are non-negative integers and that numbers are always composed of consecutive digits (without commas, for example). For example:
```
    largestNumber("I saw 3 dogs, 17 cats, and 14 cows!")
```
returns 17 (the int value 17, not the string "17"). And
```
    largestNumber("One person ate two hot dogs!")
```
returns None (the value None, not the string "None").

longestSubpalindrome(s)
Write the function longestSubpalindrome(s), that takes a string s and returns the longest palindrome that occurs as consecutive characters (not just letters, but any characters) in s. So:
```
   longestSubpalindrome("ab-4-be!!!") 
```
returns "b-4-b". If there is a tie, return the lexicographically larger value -- in Python, a string s1 is lexicographically greater than a string s2 if (s1 > s2). So:
```
   longestSubpalindrome("abcbce") 
```
returns "cbc", since ("cbc" > "bcb"). Note that unlike the previous functions, this function is case-sensitive (so "A" is not treated the same as "a" here). Also, from the explanation above, we see that longestSubpalindrome("aba") is "aba", and longestSubpalindrome("a") is "a".

longestCommonSubstring(s1, s2)
Write the function, longestCommonSubstring(s1, s2), that takes two possibly-empty strings and returns the longest string that occurs in both strings (and returns the empty string if either string is empty). For example:
```
     longestCommonSubstring("abcdef", "abqrcdest") returns "cde"
     longestCommonSubstring("abcdef", "ghi") returns "" (the empty string)
```
If there are two or more longest common substrings, return the lexicographically smaller one (ie, just use "<" to compare the strings). So, for example:
```
    longestCommonSubstring("abcABC", "zzabZZAB") returns "AB" and not "ab"
```

leastFrequentLetters(s)
Write the function leastFrequentLetters(s), that takes a string s, and ignoring case (so "A" and "a" are treated the same), returns a lowercase string containing the least-frequent alphabetic letters that occur in s, each included only once in the result and then in alphabetic order. So:
```
   leastFrequentLetters("aDq efQ? FB'daf!!!") 
```
returns "be". Note that digits, punctuation, and whitespace are not letters! Also note that seeing as we have not yet covered lists, sets, maps, or efficiency, you are not expected to write the most efficient solution. Finally, if s does not contain any alphabetic characters, the result should be the empty string ("").

replace(s1, s2, s3)
Without using the builtin method s.replace(), write its equivalent. Specifically, write the function replace(s1, s2, s3) that returns a string equal to s1.replace(s2, s3), but again without calling s.replace().

encodeOffset(s, d)
Write the function encodeOffset(s, d) that takes a string and a possibly-negative int offset d (for "delta"), and returns the string formed by replacing each letter in s with the letter d steps away in the alphabet. So: encodeOffset("ACB", 1) return "BDC" encodeOffset("ACB", 2) return "CED" This works with wraparound, so: encodeOffset("XYZ", 1) returns "YZA" And with negative offsets, so: encodeOffset("ABC", -1) returns "ZAB" And the wraparound repeats with d>26, so: encodeOffset("ABC", -27) returns "ZAB" And it is case-preserving, so: encodeOffset("Abc", -27) returns "Zab" And it does not affect non-alphabetic characters (non-letters), so: encodeOffset("A2b#c", -27) returns "Z2a#b"

decodeOffset(s, d)
Write the function decodeOffset(s, d) that takes a string that was encoded by encodeOffset using the given offset d, and returns the original string.