LeetCode 10.7 Combination Sum

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T. 

The same repeated number may be chosen from C unlimited number of times.

Note:

• All numbers (including target) will be positive integers.
• Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
• The solution set must not contain duplicate combinations.

For example, given candidate set 2,3,6,7 and target 7, 
A solution set is: 
[7] 
[2, 2, 3]

import java.util.Stack;
public class T3 {
public static void main(String[] args) {
int[] arr= {2 ,3 ,6 ,7};
T3 t=new T3();
t.DFS(arr, 7);
t.print();
}
Stack<int [] > ans=new Stack<>();
int n=0;
int[] f=new int[1000];
int pre=0;
void DFS(int[] v,int sum){
if(sum==0){
int[] arr=new int[n]; 
for(int i=0;i<n;i++){
arr[i]=f[i];
}
ans.push(arr);
}else{
for(int i=pre;i<v.length;i++){
if(sum-v[i]>=0){
pre=i;
f[n++]=v[i];
DFS(v,sum-v[i]);
n--;
}
}
}
}
void print(){
int num=1;
while(!ans.isEmpty()){
System.out.println("======"+num+"=====");
int []temp=ans.pop();
for(int i=0;i<temp.length;i++){
System.out.print(temp[i]+" ");
}
System.out.println();
num++;
}
}
}