Created
June 4, 2013 12:53
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reorder: imperative vs functional
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| type l_str = List[String] | |
| type extract = (String, l_str) | |
| def reorder(list: l_str, before: Int, after: Int): l_str = { | |
| val (value, temp_list) = delete_at(before, list) | |
| insert_at(value, after, temp_list) | |
| } | |
| def delete_at(at: Int, down: l_str, top: l_str = Nil): extract = | |
| if (at <= 0 || down.tail.isEmpty) (down.head, rewind(top, down.tail)) | |
| else delete_at(at-1, down.tail, down.head :: top) | |
| def insert_at(value: String, at: Int, down: l_str, top: l_str = Nil): l_str = | |
| if (at <= 0 || down.isEmpty) rewind(top, value :: down) | |
| else insert_at(value, at-1, down.tail, down.head :: top) | |
| def rewind(top: l_str, down: l_str): l_str = | |
| if (top.isEmpty) down else rewind(top.tail, top.head :: down) | |
| def view(list: l_str): String = list.reduce(_ + ", " + _) | |
| val a = List("a","b","c","d","e","f","g") | |
| val b = reorder(a, 1, 4) | |
| val c = reorder(b, 4, 1) | |
| val d = reorder(a, 5, 2) | |
| val e = reorder(d, 2, 5) | |
| println(view(a)) | |
| println(view(b)) | |
| println(view(c)) | |
| println(view(d)) | |
| println(view(e)) |
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| public class Shift { | |
| public static void reorder(String[] a, int i, int j) { | |
| if (i == j || i < 0 || j < 0 || i >= a.length || j >= a.length) return; | |
| if (i < j) { | |
| while(i < j) { | |
| swap(a, i, i+1); | |
| i++; | |
| } | |
| } else { | |
| while(j < i) { | |
| swap(a, i, i-1); | |
| i--; | |
| } | |
| } | |
| } | |
| public static void swap(String[] a, int i, int j) { | |
| String s = a[i]; | |
| a[i] = a[j]; | |
| a[j] = s; | |
| } | |
| public static String view(String[] argv) { | |
| StringBuilder b = new StringBuilder(); | |
| for(String s : argv) { | |
| b.append(s); | |
| b.append(", "); | |
| } | |
| return b.substring(0, b.length()-2); | |
| } | |
| public static void main(String[] argv) { | |
| String[] array = {"a","b","c","d","e","f","g"}; | |
| System.out.println(view(array)); | |
| reorder(array, 1, 4); | |
| System.out.println(view(array)); | |
| reorder(array, 4, 1); | |
| System.out.println(view(array)); | |
| reorder(array, 5, 2); | |
| System.out.println(view(array)); | |
| reorder(array, 2, 5); | |
| System.out.println(view(array)); | |
| } | |
| } |
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