39. Combination Sum
iven a set of candidate numbers (C) (without duplicates) 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.
- 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] ]
和前面的subsets
的思路基本是一致的,只是要添加一個判斷,向結果裏添加元素的時候,要滿足和爲
target
;還需要使用
i
而不是
i+1
,因爲可以使用重複的元素。
class Solution {
public List<List<Integer>> combinationSum(int[] nums, int target) {
List<List<Integer>> list = new ArrayList<>();
Arrays.sort(nums);
backtrack(list, new ArrayList<>(), nums, target, 0);
return list;
}
private void backtrack(List<List<Integer>> list, List<Integer> tempList, int [] nums, int remain, int start){
if(remain < 0) return;
else if(remain == 0) list.add(new ArrayList<>(tempList));
else{
for(int i = start; i < nums.length; i++){
tempList.add(nums[i]);
backtrack(list, tempList, nums, remain - nums[i], i); // not i + 1 because we can reuse same elements
tempList.remove(tempList.size() - 1);
}
}
}
}