How to Calculate all Unique Combinations of a Target using Backtracking in Java
The challenge
Given an array of distinct integers candidates
and a target integer target
, return a list of all unique combinations of candidates
where the chosen numbers sum to target
. You may return the combinations in any order.
The same number may be chosen from candidates
an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different.
Example 1:
Input: candidates = [2,3,6,7], target = 7 Output: [[2,2,3],[7]] Explanation: 2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate, and 7 = 7. These are the only two combinations.
Example 2:
Input: candidates = [2,3,5], target = 8 Output: [[2,2,2,2],[2,3,3],[3,5]]
Example 3:
Input: candidates = [2], target = 1 Output: []
Example 4:
Input: candidates = [1], target = 1 Output: [[1]]
Example 5:
Input: candidates = [1], target = 2 Output: [[1,1]]
Constraints:
1 <= candidates.length <= 30
1 <= candidates[i] <= 200
- All elements of
candidates
are distinct. 1 <= target <= 500
The solution in Java code
This problem is perform for using a backtracking
algorithm to solve it.
Backtracking is an algorithmic-technique for solving problems recursively by trying to build a solution incrementally, one piece at a time, removing those solutions that fail to satisfy the constraints of the problem at any point of time (by time, here, is referred to the time elapsed till reaching any level of the search tree).
geeksforgeeks.org
Using this technique, we can write the following code to solve our challenge:
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