LeetCode-77-Combinations(回溯法)-Medium

public class Solution {
private ArrayList<ArrayList<Integer>> ans= new ArrayList<ArrayList<Integer>>();

private void process(ArrayList<Integer> list, int[] nums, int initPos, int n){
if(n==0){
ans.add(list);
return;
}

if(initPos==nums.length){
return;
}

for(int i=initPos; i<nums.length; i++){
ArrayList<Integer> tList= new ArrayList(list);
tList.add(new Integer(nums[i]));
process(tList, nums, i+1, n-1);
}
}

public List<List<Integer>> combine(int n, int k) {
int[] nums= new int
;
for(int i=1; i<=n; i++){
nums[i-1]=i;
}

ArrayList<Integer> list=new ArrayList<Integer>();
process(list, nums, 0, k);

return (List)ans;
}
}