Leetcode-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, … , a_k) must be in non-descending order. (ie, a₁ ≤ a₂ ≤ … ≤ a_k).
• 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]

Solution:

A recursive method.

public class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        List<List<Integer>> resSet = new ArrayList<List<Integer>>();
        List<Integer> curRes = new ArrayList<Integer>();
        if (candidates.length==0) return resSet;
        Arrays.sort(candidates);
        int cur=0,end=candidates.length-1;
        for (int i=0;i<candidates.length;i++)
            if (candidates[i]>target){
                end = i-1;
                break;         
            }
         

        sumRecur(candidates,cur,end,target,resSet,curRes);

        return resSet;
    }


    public void sumRecur(int[] candidates, int cur, int end, int valLeft, List<List<Integer>> resSet, List<Integer> curRes){
        if (valLeft==0){
            List<Integer> temp = new ArrayList<Integer>();
            temp.addAll(curRes);
            resSet.add(temp);
            return;
        }

        if (valLeft>= candidates[cur]){
            curRes.add(candidates[cur]);
            sumRecur(candidates,cur,end,valLeft-candidates[cur],resSet,curRes);
            curRes.remove(curRes.size()-1);
        }

        if (cur<end){
            sumRecur(candidates,cur+1,end,valLeft,resSet,curRes);
        }
    }
}