一个用于产生全排列的java类代码,调用非常简单
全排列定义:从n个不同元素中任取m(m≤n)个元素,按照一定的顺序排列起来,叫做从n个不同元素中取出m个元素的一个排列。当m=n时所有的排列情况叫全排列。
// Permute.java -- A class generating all permutations import java.util.Iterator; import java.util.NoSuchElementException; import java.lang.reflect.Array; public class Permute implements Iterator { private final int size; private final Object [] elements; // copy of original 0 .. size-1 private final Object ar; // array for output, 0 .. size-1 private final int [] permutation; // perm of nums 1..size, perm[0]=0 private boolean next = true; // int[], double[] array won't work :-( public Permute (Object [] e) { size = e.length; elements = new Object [size]; // not suitable for primitives System.arraycopy (e, 0, elements, 0, size); ar = Array.newInstance (e.getClass().getComponentType(), size); System.arraycopy (e, 0, ar, 0, size); permutation = new int [size+1]; for (int i=0; i<size+1; i++) { permutation [i]=i; } } private void formNextPermutation () { for (int i=0; i<size; i++) { // i+1 because perm[0] always = 0 // perm[]-1 because the numbers 1..size are being permuted Array.set (ar, i, elements[permutation[i+1]-1]); } } public boolean hasNext() { return next; } public void remove() throws UnsupportedOperationException { throw new UnsupportedOperationException(); } private void swap (final int i, final int j) { final int x = permutation[i]; permutation[i] = permutation [j]; permutation[j] = x; } // does not throw NoSuchElement; it wraps around! public Object next() throws NoSuchElementException { formNextPermutation (); // copy original elements int i = size-1; while (permutation[i]>permutation[i+1]) i--; if (i==0) { next = false; for (int j=0; j<size+1; j++) { permutation [j]=j; } return ar; } int j = size; while (permutation[i]>permutation[j]) j--; swap (i,j); int r = size; int s = i+1; while (r>s) { swap(r,s); r--; s++; } return ar; } public String toString () { final int n = Array.getLength(ar); final StringBuffer sb = new StringBuffer ("["); for (int j=0; j<n; j++) { sb.append (Array.get(ar,j).toString()); if (j<n-1) sb.append (","); } sb.append("]"); return new String (sb); } //code from http://www.75271.com/codes/ public static void main (String [] args) { for (Iterator i = new Permute(args); i.hasNext(); ) { final String [] a = (String []) i.next(); System.out.println (i); } } }