排列组合算法

采用递归、回溯方法：


//排列组合




private static void combine(int n)...{


boolean[] selected=new boolean
;


Arrays.fill(selected, false);


int[] v=new int
;


Arrays.fill(v, -1);


doCombine(selected,v,n,0);


}




//selected 已选择标识


//filledCount 已填充个数




private static void doCombine(boolean[] selected, int[] v, int n, int filledCount)...{




for(int i=filledCount;i<n;i++)...{




for(int j=0;j<n;j++)...{




if(!selected[j])...{


selected[j]=true;


v[i]=j+1;






if(i==n-1)...{


dumpIfFullFilled(v);


}




doCombine(selected,v,n,i+1);




//回溯


selected[j]=false;


v[i]=-1;


}


}




}


}






private static void dumpIfFullFilled(int[] v)...{


String s="";




for(int i=0;i<v.length;i++)...{




if(v[i]==-1)...{


return;


}


s+=v[i]+" ";


}


System.out.println(s);


}



测试

combine(4);

输出

1 2 3 4
1 2 4 3
1 3 2 4
1 3 4 2
1 4 2 3
1 4 3 2
2 1 3 4
2 1 4 3
2 3 1 4
2 3 4 1
2 4 1 3
2 4 3 1
3 1 2 4
3 1 4 2
3 2 1 4
3 2 4 1
3 4 1 2
3 4 2 1
4 1 2 3
4 1 3 2
4 2 1 3
4 2 3 1
4 3 1 2
4 3 2 1