LeetCode : Combination Sum II [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.

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]

思路：回溯算法，注意跳過相同元素。

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

public class Solution {
	public List<List<Integer>> combinationSum2(int[] candidates, int target) {
		List<List<Integer>> result = new ArrayList<List<Integer>>();
		List<Integer> current = new ArrayList<Integer>();
		Arrays.sort(candidates);
		solve(candidates, target, 0, current, result);
		return result;
	}

	public void solve(int[] candidates, int target, int index, List<Integer> current, List<List<Integer>> result) {
		if (target == 0) {
			List<Integer> tmp = new ArrayList<Integer>(current);
			result.add(tmp);
			return;
		}
		for (int i = index; i < candidates.length; i++) {
			if (target < candidates[i]) {
				return;
			}
			current.add(candidates[i]);
			solve(candidates, target - candidates[i], i + 1, current, result);
			current.remove(current.size() - 1);
			while(i<(candidates.length-1)&&candidates[i]==candidates[i+1]){
                i++;
            }
		}
	}
}