Combination Sum II Combinations

https://leetcode.com/problems/combination-sum-ii/

 

 题目跟前面几道题很类似，直接写代码：

class Solution {
public:
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        sort(candidates.begin(),candidates.end());
        if(candidates.size()==0)
            return res;
        vector<int> temp;
        helper(candidates,0,target,temp);
        return res;
        
        
    }
private:
    void helper(vector<int>& candidates,int index,int target,vector<int>& temp){
        if(target==0)
            res.push_back(temp);
        
        if(target<0 || index>=candidates.size()){
            return;
        }
            
        for(int i=index;i<candidates.size();i++)
        {
            if(i>index && candidates[i]==candidates[i-1])//必须保证第一个位置以一个数值递归下去时不能重复！但第一次遍历时又必须保存，所以必须写成i>index,而不是i>0！！就是针对这类情形 1,1，2,5,6,7,10  8    【1,2,5】 【1,2,5】 【1,1,6】
                continue;
            temp.push_back(candidates[i]);
            helper(candidates,i+1,target-candidates[i],temp);//注意这个地方就不应该是index了，而应该传入i+1，否则，会出现降序数列
            temp.pop_back();
        }
    }
private:
    vector<vector<int>> res;
};

 https://leetcode.com/problems/combinations/

 

class Solution {
public:
    vector<vector<int>> combine(int n, int k) {
        if(n<k)
            return res;
        vector<int> temp;
        helper(n,1,k,temp,k);
        return res;
    }
  
    void helper(int n,int pos,int k,vector<int>& temp,int count){
        if(0==count){
            res.push_back(temp);
            return;
        }
        if(pos>n||count<0)
            return;
        for(int i=pos;i<=n;i++){
            temp.push_back(i);
            helper(n,i+1,k,temp,--count);//这个地方写成i+1而不是pos+1
            temp.pop_back();
            count++;
        }
    }
    
private:
    vector<vector<int>> res;
};