【leetcode刷题笔记】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 toT.

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] 

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跟Combination Sum的差别就是上面红色的那行字，只要把递归时候的起点由i改为i+1即可，参见下列代码中高亮的部分：

代码如下：

public class Solution {
    private void combiDfs(int[] candidates,int target,List<List<Integer>> answer,List<Integer> numbers,int start){
        if(target == 0){
            answer.add(new ArrayList<Integer>(numbers));
            return;
        }
        
        int prev = -1;
        
        for(int i = start;i < candidates.length;i++){
            if(candidates[i] > target)
                break;
            if(prev != -1 && prev == candidates[i])
                continue;
            
            numbers.add(candidates[i]);
            combiDfs(candidates, target-candidates[i], answer, numbers,i+1);
            numbers.remove(numbers.size()-1);
            
            prev = candidates[i];
        }
    }
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        List<List<Integer>> answer = new ArrayList<List<Integer>>();
        List<Integer> numbers = new ArrayList<Integer>();
        Arrays.sort(candidates);
        combiDfs(candidates, target, answer, numbers,0);
        
        return answer;
        
    }
}