Combination Sum II

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.

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

Note:

  • All numbers (including target) will be positive integers.
  • 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. [
  2.   [1, 7],
  3.   [1, 2, 5],
  4.   [2, 6],
  5.   [1, 1, 6]
  6. ]

Solution:

  1. public class Solution {
  2.   public List<List<Integer>> combinationSum2(int[] candidates, int target) {
  3.     Arrays.sort(candidates);
  4.     List<List<Integer>> res = new ArrayList<List<Integer>>();
  5.     helper(candidates, target, 0, new ArrayList<Integer>(), res);
  6.     return res;
  7.   }
  9.   private void helper(int[] candidates, int target, int index, List<Integer> sol, List<List<Integer>> res) {
  10.     if (target == 0) {
  11.       res.add(new ArrayList<Integer>(sol));
  12.       return;
  13.     }
  15.     if (target < 0 || index == candidates.length) {
  16.       return;
  17.     }
  19.     for (int i = index; i < candidates.length; i++) {
  20.       if (i > index && candidates[i] == candidates[i - 1]) {
  21.         continue;
  22.       }
  24.       sol.add(candidates[i]);
  25.       helper(candidates, target - candidates[i], i + 1, sol, res);
  26.       sol.remove(sol.size() - 1);
  27.     }
  28.   }
  29. }