全排列算法--递归实现(Java)

　　//对数组array从索引为start到最后的元素进行全排列
publicvoid 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privateint[][] result;
    
    public Permutation(int[] array) {
        this.row = 0;
        this.result = newint[this.factor(array.length)][array.length];
    }
    
    publicint[][] getResult() {
        return result;
    }

    //求数组a的逆序数publicint 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publicint factor(int a) {
        int r = 1;
        for (; a>=1; a--) {
            r *= a;
        }
        return r;
    }

    publicvoid 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);
            }
        }
    } 
    
    publicvoid swap(int[] array,int s,int i) {
        int t=array[s];
        array[s]=array[i];
        array[i]=t;
    }
    
    publicvoid printResult() {
        for (int i = 0; i < result.length; i++) {
                System.out.println(Arrays.toString(this.result[i]));
        }
    }
    
    publicstaticvoid main(String[] args) {
        int[] a = {1, 2, 3};
        Permutation p = new Permutation(a);
        p.perm(a,0);
        p.printResult();
    }
}

1: 1 2 3 逆序数是：0

2: 1 3 2 逆序数是：1

3: 2 1 3 逆序数是：1

4: 2 3 1 逆序数是：2

5: 3 2 1 逆序数是：3

6: 3 1 2 逆序数是：2

[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 2, 1]
[3, 1, 2]