Combination Sum II LeetCode

 Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to target.


Each number in candidates may only be used once in the combination.


Note: The solution set must not contain duplicate combinations.


 


Example 1:


Input: candidates = [10,1,2,7,6,1,5], target = 8

Output: 

[

[1,1,6],

[1,2,5],

[1,7],

[2,6]

]

Example 2:


Input: candidates = [2,5,2,1,2], target = 5

Output: 

[

[1,2,2],

[5]

]




class Solution {
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
       List<List<Integer>> result = new ArrayList<>();
       Arrays.sort(candidates);
        backtrack(candidates, 0, target, new ArrayList<>(), result);
        return result;
    }
      private void backtrack(int[] candidates, int start, int target, List<Integer> path, List<List<Integer>> result) {
        // Base case: target exactly zero
        if (target == 0) {
            result.add(new ArrayList<>(path)); // Add a copy of the current path
            return;
        }

        // Base case: target becomes negative (invalid path)
        if (target < 0) {
            return;
        }

        // Explore further by trying all candidates starting from 'start' index
        for (int i = start; i < candidates.length; i++) {
       
        if(i > start && candidates[i]==candidates[i-1]) continue;
       
            path.add(candidates[i]); // Choose
            backtrack(candidates, i+1, target - candidates[i], path, result); // Not i+1 because reuse allowed
            path.remove(path.size() - 1); // Backtrack
        }
}
}

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