Add reverse-string approaches

exercises/practice/reverse-string/.approaches/config.json

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+{
+  "approaches": [
+    {
+      "uuid": "5e6c8ae8-7cd0-4500-bc1b-e21f036eb708",
+      "slug": "reversing-list",
+      "title": "Reversing a List of Characters",
+      "blurb": "Explode the string into a list of characters and reverse it",
+      "authors": [
+        "BNAndras"
+      ]
+    },
+    {
+      "uuid": "92f3c425-7696-4759-88dc-07ebe2c2f249",
+      "slug": "reversing-with-substrings",
+      "title": "Reversing with Substrings",
+      "blurb": "Reverse the string with recursion and substrings",
+      "authors": [
+        "BNAndras"
+      ]
+    },
+    {
+      "uuid": "b7c8e68e-69f7-4e14-be0c-3191f57fb3b4",
+      "slug": "reversing-by-index",
+      "title": "Reversing by Index",
+      "blurb": "Reverse the string by iterating backwards",
+      "authors": [
+        "BNAndras"
+      ]
+    }
+  ]
+}

exercises/practice/reverse-string/.approaches/introduction.md

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+# Introduction
+
+There are several idiomatic ways to solve this exercise.
+
+## Approach: Reversing a list of characters
+
+```scheme
+(define (my-reverse s)
+    (list->string (foldl cons '() (string->list s))))
+```
+
+For more information, check the [reversing a list of characters approach][approach-reversing-list].
+
+## Approach: Reversing with substrings
+
+```scheme
+(define (my-reverse s)
+  (if (non-empty-string? s)
+      (string-append (my-reverse (substring s 1))
+                     (substring s 0 1))
+      ""))
+```
+
+For more information, check the [reversing with substrings approach][approach-reversing-substrings].
+
+## Approach: Reversing by index
+
+```scheme
+(define (my-reverse s)
+  (define end (sub1 (string-length s)))
+  (build-string (add1 end)
+                (λ (i) (string-ref s (- end i)))))
+```
+
+For more information, check the [reversing by index approach][approach-reversing-by-index].
+
+
+[approach-reversing-list]:          https://exercism.org/tracks/racket/exercises/reverse-string/approaches/reversing-list
+[approach-reversing-substrings]:    https://exercism.org/tracks/racket/exercises/reverse-string/approaches/reversing-substrings
+[approach-reversing-by-index]:      https://exercism.org/tracks/racket/exercises/reverse-string/approaches/reversing-by-index

exercises/practice/reverse-string/.approaches/reversing-by-index/content.md

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+# Reversing by Index
+
+```scheme
+(define (my-reverse s)
+  (define end (sub1 (string-length s)))
+  (build-string (add1 end)
+                (λ (i) (string-ref s (- end i)))))
+```

exercises/practice/reverse-string/.approaches/reversing-by-index/snippet.txt

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+(define (my-reverse s)
+  (define end (sub1 (string-length s)))
+  (build-string (add1 end)
+                (λ (i) (string-ref s (- end i)))))

exercises/practice/reverse-string/.approaches/reversing-list/content.md

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+# Reversing a List of Characters
+
+```scheme
+(define (my-reverse s)
+    (list->string (foldl cons '() (string->list s))))
+```

exercises/practice/reverse-string/.approaches/reversing-list/snippet.txt

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+(define (my-reverse s)
+    (list->string (foldl cons '() (string->list s))))

exercises/practice/reverse-string/.approaches/reversing-substrings/content.md

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+# Reversing with Substrings
+
+```scheme
+(define (my-reverse s)
+  (if (non-empty-string? s)
+      (string-append (my-reverse (substring s 1))
+                     (substring s 0 1))
+      ""))
+```

exercises/practice/reverse-string/.approaches/reversing-substrings/snippet.txt

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+(define (my-reverse s)
+  (if (non-empty-string? s)
+      (string-append (my-reverse (substring s 1))
+                     (substring s 0 1))
+      ""))