• Postponed

• Text questions: Strings, Exercises 10

  • Hints:

    • Here is a spec for the desired function.

      countMatches 2 arguments: A non-empty string and any other string Return: A non-negative integer, the number of times arg1 appears as a substring of arg2.

      Example calls:

          countMatches("a", "Hawaii") --> 2
          countMatches("h", "Hawaii") --> 0
          countMatches("wa", "Hawaii") --> 1
          countMatches("h", "") --> 0
      

    • Here are two approaches to solving this problem.

      1. Approach #1

         • Use an index as a loop control variable in a for loop.

         • For each index position in the string arg2, use == to compare arg1 to a slice of arg2 that begins at that index and continues for the length of arg1. (Add that length to that index to find the end of the slice.)

         • Use an accumulator to count the number of matches found.

      2. Approach #2

         • Use a while loop whose guard uses the string find() method.

           str.find 2 arguments: A string and an integer indicating a position in an string object (e.g., an index). If arg2 is missing, that second argument is treated as 0. Return: An integer, the lowest integer where arg1 appears in a string object, starting the search at position arg2. Return -1 if arg1 does not appear in that string object.

           Example calls:

               "Mississippi".find("is") --> 1
               "Mississippi".find("is", 2) --> 4
               "Mississippi".find("it") --> -1
               "Mississippi".find("is", 5) --> -1
           

           Notes:

           • In this spec, "a string object" refers to the string whose method is being called, e.g., "Mississippi".

           • The type str is a built-in type in Python3, so no import statement is necessary in order to use this method.

         • For that while loop, initialize a variable position at 0, and also use an accumulator to count the matches found so far. If the find() method detects match (in the guard of that while loop), add 1 to the count and change the position to just after the location where that match was found.

Recursion questions, 10f, 11c

Recursion questions, 12 c

Conditional questions, 2g