Leetcode039-combiantionSum

Description

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

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

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

Example

Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
  [7],
  [2,2,3]
]

Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]

Solution

class Solution {
    public void backtracking(List<List<Integer>> res, List<Integer> tmp, int[] nums, int target, int start, int sum){
        if (sum == target){
            res.add(new ArrayList<Integer>(tmp));
            return;
        }
        for (int i = start; i < nums.length; i++){
            tmp.add(nums[i]);
            if (sum + nums[i] <= target) backtracking(res, tmp, nums, target, i, sum + nums[i]);
            else{
                tmp.remove(tmp.size()-1);
                return;
            }
            tmp.remove(tmp.size()-1);            
        }
    }
    
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        List<List<Integer>> res = new ArrayList<>();
        if (candidates == null) return res;
        Arrays.sort(candidates);
        backtracking(res, new ArrayList<Integer>(), candidates, target, 0, 0);
        return res;
    }
}

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