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.

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

Example
Given candidate set [10,1,6,7,2,1,5] and target 8,

A solution set is:

[
  [1,7],
  [1,2,5],
  [2,6],
  [1,1,6]
]
Note
All numbers (including target) will be positive integers.
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.
 */
public class CombinationSumII {

    /**
     * @param num: Given the candidate numbers
     * @param target: Given the target number
     * @return: All the combinations that sum to target
     */
    public List<List<Integer>> combinationSum2(int[] num, int target) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        Arrays.sort(num);
        dfs(result, new ArrayList<Integer>(), num, 0, target);
        return result;
    }

    public void dfs(List<List<Integer>> result, List<Integer> list, 
            int[] num, int position, int target) {
        if (target == 0) {
            result.add(new ArrayList<Integer>(list));
            return;
        }
        for (int i = position; i < num.length && target > 0; ++i) {
            if (i > position && num[i] == num[i - 1]) {
                continue;
            }
            list.add(num[i]);
            dfs(result, list, num, i + 1, target - num[i]);
            list.remove(list.size() - 1);
        }
    }

}