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.
  • 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] 

Solution

Similar to Combination Sum I, except for line * && **.

public class Solution {
    public List<List<Integer>> combinationSum2(int[] num, int target) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        Arrays.sort(num);
        ArrayList<Integer> path = new ArrayList<Integer>();
        combinationSumRe(num, target, 0, path, res);
        return res;
    }
    void combinationSumRe(int[] candidates, int target, int start, ArrayList<Integer> path, List<List<Integer>> res) {
        if (target == 0) {
            ArrayList<Integer> p = new ArrayList<Integer>(path);
            res.add(p);
            return;
        }
        for (int i = start; i < candidates.length && target >= candidates[i]; ++i) {
            if (i!=start && candidates[i-1] == candidates[i]) continue; // *
            path.add(candidates[i]);
            combinationSumRe(candidates, 
                             target-candidates[i], i+1, path, res); // **
            path.remove(path.size() - 1);
        }
    }
}