LeetCode/java/combination-sum-ii.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;

class Solution {
  int[] candidates;
  private HashSet<List<Integer>> combinations;

  private void combinationSum2(ArrayList<Integer> combination, int target, int i0) {
    if (target == 0) {
      combinations.add(combination.stream().toList());
      return;
    }

    if (i0 >= candidates.length) {
      return;
    }

    for (int i = i0; i < candidates.length && candidates[i] <= target; ++i) {
      if (i > i0 && candidates[i] == candidates[i - 1]) {
        continue;
      }

      combination.addLast(candidates[i]);
      combinationSum2(combination, target - candidates[i], i + 1);
      combination.removeLast();
    }
  }

  public List<List<Integer>> combinationSum2(int[] candidates, int target) {
    this.candidates = candidates;
    combinations = new HashSet<>();

    Arrays.sort(this.candidates);
    combinationSum2(new ArrayList<>(), target, 0);
    var result = combinations.stream().toList();

    return result;
  }
}