LeetCode216: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]]

这道题就相当于前面 Combination Sum II 中candidates这个数组是由1-9这9个数字组成的数组，并且对路径的长度做了要求，路径的长度是k，解题思路还是一样的。
runtime:0ms

class Solution {
public:
    vector<vector<int>> combinationSum3(int k, int n) {
        vector<int> path;
        vector<vector<int>> result;
        helper(k,n,0,1,path,result);
        return result;
    }

    void helper(int k,int target,int base,int pos,vector<int> & path,vector<vector<int>> &result)
    {
        if(k==0&&base==target)
        {
            result.push_back(path);
            return ;
        }
        if(k<0||base>target)
            return ;
        for(int i=pos;i<=9;i++)
        {
            path.push_back(i);
            helper(k-1,target,base+i,i+1,path,result);
            path.pop_back();
        }
    }
};