数组 m选n 组合

第一种：

public class Combine {private static ArrayList <Integer>tmpArr = new ArrayList<>();public static void main(String[] args) {int [] com = {1,2,3,4,5,6,7,8};int k = 8;if(k > com.length || com.length <= 0){return ;}combine(0 ,k ,com);}public static void combine(int index,int k,int []arr) {if(k == 1){for (int i = index; i < arr.length; i++) {tmpArr.add(arr[i]);System.out.println(tmpArr.toString());tmpArr.remove((Object)arr[i]);}}else if(k > 1){for (int i = index; i <= arr.length - k; i++) {tmpArr.add(arr[i]);combine(i + 1,k - 1, arr);tmpArr.remove((Object)arr[i]);}}else{return ; }}}

第二种：

public static void main(string args[]){

String[] str = { "3.2", "2.1", "1.8","4.5"}; 

        getNext(null, str, 4);  
        System.out.println(list66);

}

private static List<String> list66 = new ArrayList<String>();
public static void getNext(String begin, String[] s, int num) {  

if (num > 1) {  
for (int i = 0; i < s.length - num+1; i++) {  
//取出一个字符  
String  str = s[i];  
//数组后边的元素组成新数组  
String[] newS = Arrays.copyOfRange(s, i + 1, s.length);  
//递归，从后面的n-1个数种选出num-1个  
getNext(begin == null ? str : (begin + "*" + str), newS,num - 1);  
}  
} else {  
//如果从剩下的s中选出1个数，那么前缀依次和s中的所有元素组合一次  
for (int b = 0; b < s.length; b++) {  
list66.add(begin + "*" + s[b]);  
}  
}
 
}