JAVA用递归实现全排列算法的示例代码

//对数组array从索引为start到最后的元素进行全排列  public void perm(int[]array,int start) {
    if(start==array.length) { //出口条件
      for(int i=0;i<array.length;i++) {
//        this.result[row][i] = array[i];
        System.out.print(array[i]+" ");
      }
//      System.out.print(++this.row+": ");
//      System.out.println("逆序数是："+ this.against(array));
      System.out.print('\n');
    }
    else {
      for(int i=start;i<array.length;i++) {
        swap(array,start,i); //交换数组array中索引为start与i的两个元素
        perm(array,start+1); 
        swap(array,start,i);
      }
    }
  }

package matrix;

import java.util.Arrays;

public class Permutation {

  /**
   * author:ZhaoKe
   * college: CUST
   */
  //当前打印的第几个排列
  private int row = 0;
  //存储排列的结果
  private int[][] result;
  
  public Permutation(int[] array) {
    this.row = 0;
    this.result = new int[this.factor(array.length)][array.length];
  }
  
  public int[][] getResult() {
    return result;
  }

  //求数组a的逆序数
  public int against(int a[]) {
    int nn = 0;
    for (int i = 0; i < a.length-1; i++) {
      for (int j = i+1; j<a.length; j++) {
        if (a[i] > a[j]) {
          nn++;
        }
      }
    }
    return nn;
  }

  //排列数
  public int factor(int a) {
    int r = 1;
    for (; a>=1; a--) {
      r *= a;
    }
    return r;
  }

  public void perm(int[]array,int start) {
    if(start==array.length) {
      System.out.print((this.row+1)+": ");
      for(int i=0;i<array.length;i++) {
        this.result[row][i] = array[i];
        System.out.print(array[i]+" ");
      }
      this.row++;
      System.out.println("逆序数是："+ this.against(array));
      System.out.print('\n');
    }
    else {
      for(int i=start;i<array.length;i++) {
        swap(array,start,i);
        perm(array,start+1);
        swap(array,start,i);
      }
    }
  } 
  
  public void swap(int[] array,int s,int i) {
    int t=array[s];
    array[s]=array[i];
    array[i]=t;
  }
  
  public void printResult() {
    for (int i = 0; i < result.length; i++) {
        System.out.println(Arrays.toString(this.result[i]));
    }
  }
  
  public static void main(String[] args) {
    int[] a = {1, 2, 3};
    Permutation p = new Permutation(a);
    p.perm(a,0);
    p.printResult();
  }
}