cs330_f2016:racketlists
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cs330_f2016:racketlists [2016/08/31 18:49] morse |
cs330_f2016:racketlists [2021/06/30 23:42] (current) |
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| * Natural recursion | * Natural recursion | ||
| * Common patterns for recursive list-processing operations | * Common patterns for recursive list-processing operations | ||
| - | * Using auxiliary variables | + | * Using auxiliary parameters |
| ---- | ---- | ||
| Line 17: | Line 17: | ||
| ====Deliverables:==== | ====Deliverables:==== | ||
| - | For this lab, you will need to implement the following functions and data structures in Racket: | + | For this lab, you will need to implement the following functions recursively in Racket: |
| * ''check-temps1'' | * ''check-temps1'' | ||
| * ''check-temps'' | * ''check-temps'' | ||
| Line 27: | Line 27: | ||
| * ''get-nth'' | * ''get-nth'' | ||
| * ''find-item'' | * ''find-item'' | ||
| + | |||
| + | ** | ||
| + | You must write all of these functions recursively (though you can use helper functions as needed). | ||
| + | |||
| + | You may not use higher-order functions like ''map'', ''filter'', or any of the variants of ''fold''. You may not use functions that use or return indices, such as ''index-of'' or ''list-ref''. | ||
| + | |||
| + | You may not use anything that modifies a value in place such as ''set!'' or list-modification operators. | ||
| + | ** | ||
| === check-temps1 === | === check-temps1 === | ||
| Line 36: | Line 44: | ||
| For example, ''(check-temps1 (list 80 92 56))'' returns true, and ''(check-temps1 (list 80 99 56))'' returns false. | For example, ''(check-temps1 (list 80 92 56))'' returns true, and ''(check-temps1 (list 80 99 56))'' returns false. | ||
| - | === check-temps1 === | + | === check-temps === |
| <code racket> | <code racket> | ||
| (define (check-temps temps low high) ...) | (define (check-temps temps low high) ...) | ||
| Line 50: | Line 58: | ||
| (define (convert digits) ...) | (define (convert digits) ...) | ||
| </code> | </code> | ||
| - | where ''digits'' is a list of digits (each between 0 and 9) and the result is the integer equivalent of these interpreted as a list of digits of a number in reverse order. | + | where ''digits'' is a non-empty list of digits (each between 0 and 9) and the result is the integer equivalent of these interpreted as a list of digits of a number in reverse order. |
| For example, ''(convert (list 1 2 3))'' should return the number 321. | For example, ''(convert (list 1 2 3))'' should return the number 321. | ||
| + | |||
| + | You may not use ''string->number'' or any other string-handling functions for this. Avoid using strings at all. | ||
| + | |||
| + | Hint: Don't try to figure out what position each digit is in as you process the list. (I.e., don't worry about "hundreds place", "tens place", etc.). Can you figure out how to write the conversion with a more straightforward recursion? What should recursing on the rest of the list return if the function works correctly? What's the relationship between that and the first thing in the list that will give you the correct result? | ||
| === duple === | === duple === | ||
| Line 68: | Line 80: | ||
| (define (average lst) ...) | (define (average lst) ...) | ||
| </code> | </code> | ||
| - | where ''lst'' is a list of numbers, and the result is the average of these numbers. | + | where ''lst'' is a non-empty list of numbers, and the result is the average of these numbers. |
| - | For example, ''(average (list 1 2 3 4))'' returns 2.5. | + | For example, ''(average (list 1 2 3 4))'' returns 5/2. |
| + | |||
| + | Hint: you are **not** required to compute the average in a single pass. Can you break it into simpler operations? | ||
| === convertFC === | === convertFC === | ||
| Line 84: | Line 98: | ||
| (define (eliminate-larger lst) ...) | (define (eliminate-larger lst) ...) | ||
| </code> | </code> | ||
| - | where ''lst'' is a list of numbers, and the result is the same list but with all values larger than any subsequent ones removed. | + | where ''lst'' is a list of numbers, and the result is the same list but with **all** values larger than **any** subsequent ones removed. |
| For example, ''(eliminate-larger (list 1 2 3 9 4 5))'' returns ''(1 2 3 4 5)''. | For example, ''(eliminate-larger (list 1 2 3 9 4 5))'' returns ''(1 2 3 4 5)''. | ||
| Hint: try using a helper function. | Hint: try using a helper function. | ||
| + | |||
| + | Hint 2: consider trying to make the decision about whether to drop a particular item from the list **after** recursively calling eliminate-larger on the rest after that one -- it's easier. | ||
| === get-nth === | === get-nth === | ||
| Line 116: | Line 132: | ||
| You again **do not** need to bulletproof the code to enforce proper inputs. | You again **do not** need to bulletproof the code to enforce proper inputs. | ||
| Your code only needs to return correct values given correct inputs. | Your code only needs to return correct values given correct inputs. | ||
| + | But you should be careful to think about what the correct output should be for the case where the input list is empty. | ||
| ---- | ---- | ||
| Line 122: | Line 139: | ||
| You may want to again use the Step button to walk through your code and watch the equivalent sequence of substitutions that are performed. This is particularly useful in tracing the recursion and watching what's happening to the parameters. | You may want to again use the Step button to walk through your code and watch the equivalent sequence of substitutions that are performed. This is particularly useful in tracing the recursion and watching what's happening to the parameters. | ||
| + | |||
| + | You may use auxiliary or helper functions as needed. For many of these the simplest solution is to use multiple functions instead of trying to cram it all through one recursive pass through the list. You might also have to recurse through the list multiple times, in which case it's easiest to use separate functions. | ||
| + | |||
cs330_f2016/racketlists.1472669358.txt.gz · Last modified: 2021/06/30 23:40 (external edit)
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