Combination Sum II @LeetCode

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] 

	package leetcode.combinations;
	import java.util.ArrayList;
	import java.util.Arrays;
	/**
	* Almost same as CombinationSum I, Only difference is element can only used in combination once.
	* As there're duplicate elements, we need to make sure result with no duplidates like subsets II.
	*
	* Element used once --> helper(xxx, i+1)
	* Result without duplicates --> if(i!=position && num[i] == nums[i-1]) { continue; }
	*
	* i!=position --> only happens when backtrack, after move number1. number2 cannot be used.
	* i==position --> just add number2, not iterative it. (We don't allow number2 iteration which number1 already does)
	*
	* @author jeffwan
	* @date Feb 11, 2014
	*/
	public class CombinationSum2 {
	public static void main(String[] args) {
	int[] nums = {10, 1, 2, 7, 6, 1, 5};
	int target = 8;
	System.out.println(combinationSum2(nums,target));
	}
	public static ArrayList<ArrayList<Integer>> combinationSum2(int[] num, int target) {
	Arrays.sort(num);
	ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
	ArrayList<Integer> list = new ArrayList<Integer>();
	combinationSumHelper(result, list, num, target, 0);
	return result;
	}
	private static void combinationSumHelper(ArrayList<ArrayList<Integer>> result,
	ArrayList<Integer> list, int[] num, int target, int position) {
	int sum = 0;
	for (int x: list) {
	sum += x;
	}
	if (sum == target) {
	result.add(new ArrayList<Integer>(list));
	return;
	}
	if (sum < target) {
	for (int i = position; i<num.length; i++) {
	if ( i != position && num[i] == num[i-1]) {
	continue;
	}
	list.add(num[i]);
	combinationSumHelper(result, list, num, target, i+1);
	list.remove(list.size() - 1);
	}
	}
	}
	}

view raw CombinationSum2.java hosted with ❤ by GitHub