[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]]

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

 

继续dfs,不用判断重复。

class Solution {
public:
    void dfs(int k,int n,int val,vector<int> tmp,vector<vector<int>>& result)
    {
        if(tmp.size()==k)
        {
            int sum=0;
            for(int i=0;i<tmp.size();i++)
            {
                sum+=tmp[i];
            }
            if(sum==n) result.push_back(tmp);
            return;
        }
        for(int i=val;i<=9;i++)
        {
            tmp.push_back(i);
            dfs(k,n,i+1,tmp,result);
            tmp.pop_back();
        }
    }
    vector<vector<int>> combinationSum3(int k, int n) {
        vector<int> tmp;
        vector<vector<int>> result;
        dfs(k,n,1,tmp,result);
        return result;
    }
};