CombinationSumII.java

/**
 * Given a collection of candidate numbers (C) and a target number (T), find all unique combinations
 * in C where the candidate numbers sums to T.
 *
 * <p>Each number in C may only be used once in the combination.
 *
 * <p>Note:
 *
 * <p>All numbers (including target) will be positive integers.
 *
 * <p>Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤
 * ak). The solution set must not contain duplicate combinations. For example, given candidate set
 * 10,1,2,7,6,1,5 and target 8, A solution set is: [1, 7] [1, 2, 5] [2, 6] [1, 1, 6]
 */

import java.util.ArrayList;
import java.util.Arrays;

public class CombinationSumII {
  public ArrayList<ArrayList<Integer>> combinationSum2(int[] candidates, int target) {
    ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
    ArrayList<Integer> list = new ArrayList<Integer>();
    Arrays.sort(candidates);
    dfs(res, 0, candidates, list, target);
    return res;
  }

  private void dfs(
      ArrayList<ArrayList<Integer>> res,
      int start,
      int[] candidates,
      ArrayList<Integer> list,
      int target) {
    if (target == 0) {
      res.add(new ArrayList<Integer>(list));
      return;
    }
    int pre = -1;
    for (int i = start; i < candidates.length; i++) {
      if (pre == candidates[i]) continue;
      if (candidates[i] > target) return;
      pre = candidates[i];
      list.add(candidates[i]);
      dfs(res, i + 1, candidates, list, target - candidates[i]);
      list.remove(list.size() - 1);
    }
  }
}