LeetCode 40. Combination Sum II（组合求和）

原题网址：https://leetcode.com/problems/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] 

方法：深度优先搜索。

public class Solution {
    private void find(int[] candidates, int from, int sum, List nums, List> results) {
        if (sum == 0) {
            results.add(new ArrayList<>(nums));
            return;
        }
        if (from >= candidates.length || sum < 0 || candidates[from] > sum) return;
        for(int i=from; ifrom && candidates[i]==candidates[i-1]) continue;
            nums.add(candidates[i]);
            find(candidates, i+1, sum - candidates[i], nums, results);
            nums.remove(nums.size()-1);
        }
    }
    public List> combinationSum2(int[] candidates, int target) {
        List> results = new ArrayList<>();
        if (candidates == null) return results;
        Arrays.sort(candidates);
        find(candidates, 0, target, new ArrayList<>(), results);
        return results;
    }
}