基础算法2：Selection sort

基础算法二：Selection sort
public class Selection { // selection sort public static void sort(Comparable[] a) { int N = a.length; for (int i = 0; i < N; i++) { int min = i; for (int j = i+1; j < N; j++) { if (less(a[j], a[min])) min = j; } exch(a, i, min); assert isSorted(a, 0, i); } assert isSorted(a); } // use a custom order and Comparator interface - see Section 3.5 public static void sort(Object[] a, Comparator c) { int N = a.length; for (int i = 0; i < N; i++) { int min = i; for (int j = i+1; j < N; j++) { if (less(c, a[j], a[min])) min = j; } exch(a, i, min); assert isSorted(a, c, 0, i); } assert isSorted(a, c); } /*********************************************************************** * Helper sorting functions ***********************************************************************/ // is v < w ? private static boolean less(Comparable v, Comparable w) { return (v.compareTo(w) < 0); } // is v < w ? private static boolean less(Comparator c, Object v, Object w) { return (c.compare(v, w) < 0); } // exchange a[i] and a[j] private static void exch(Object[] a, int i, int j) { Object swap = a[i]; a[i] = a[j]; a[j] = swap; } /*********************************************************************** * Check if array is sorted - useful for debugging ***********************************************************************/ // is the array a[] sorted? private static boolean isSorted(Comparable[] a) { return isSorted(a, 0, a.length - 1); } // is the array sorted from a[lo] to a[hi] private static boolean isSorted(Comparable[] a, int lo, int hi) { for (int i = lo + 1; i <= hi; i++) if (less(a[i], a[i-1])) return false; return true; } // is the array a[] sorted? private static boolean isSorted(Object[] a, Comparator c) { return isSorted(a, c, 0, a.length - 1); } // is the array sorted from a[lo] to a[hi] private static boolean isSorted(Object[] a, Comparator c, int lo, int hi) { for (int i = lo + 1; i <= hi; i++) if (less(c, a[i], a[i-1])) return false; return true; } // print array to standard output private static void show(Comparable[] a) { for (int i = 0; i < a.length; i++) { System.out.println(a[i]); } }}

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