【leetcode】Combination Sum III

Combination Sum III

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.

Ensure that numbers within the set are sorted in ascending order.
Example 1:
Input: k = 3, n = 7
Output:

[[1,2,4]]

Example 2:
Input: k = 3, n = 9
Output:

[[1,2,6], [1,3,5], [2,3,4]]

思路：感觉和leetcode combinations那个题目很相似。只不过，在只有sum=n的时候，才加入到result这个集合中。

class Solution {
public:

    void comb(int n, int level, int k, vector<vector<int> > &result,vector<int> &temp)
    {
        int sum=0;
        for(int i=0;iif(k!=temp.size() && (n-sum)/(k-temp.size())>9) return;

        if(temp.size()==k && n==sum) //看是否取到了k个数
        {
            result.push_back(temp);
            return;
        }
        else if(temp.size()==k)
            return;

        for(int i=level+1;i<=n-sum;i++)
        {
            temp.push_back(i);
            comb(n, i, k, result, temp);
            temp.pop_back();
        }
    }

    vector<vector<int> > combinationSum3(int k, int n) {
        vector<vector<int> > res;
        if(n == 0 || k ==0 || n/k > 9) return res;
        vector<int> temp;

        for(int i=1;ireturn res;
    }
};