60. 第k个排列

 1 class Solution {
 2       int index=0;
 3      String ss="";
 4     ArrayList<Integer> ans=null;
 5       public String getPermutation(int n, int k) {
 6             int[] nums=new int[n+1];      
 7             rec(nums,k,"");
 8             return ss;
 9         }
10       public void rec(int[] nums,int k,String str)
11       {
12           if(str.length()==nums.length-1)
13           {
14               index++;
15           if(index==k)
16           {
17               ss=str;
18               return;
19           }
20           else
21               return;
22           }
23           if(index>k)
24               return;
25           for(int i=1;i<nums.length;i++)
26           {             
27               if(nums[i]==1)
28                   continue;
29               str=str+i;
30               nums[i]=1;
31               rec(nums,k,str);
32                str=str.substring(0, str.length()-1);
33               nums[i]=0;
34           }
35       }
36 }