LeetCode:Combination Sum III

Combination Sum III

Total Accepted: 34119  Total Submissions: 93255  Difficulty: Medium

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.

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.

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  (M) Combination Sum

思路：

与【Combinations】类似，稍作修改即可。

c++ code:

class Solution {
public:
    vector<vector<int>> combinationSum3(int k, int n) {
        
        vector<vector<int>> combs;
        vector<int> comb;
        combine(combs,comb,1,k,n);
        return combs;
    }
    
    // 自定义函数
    void combine(vector<vector<int>> &combs, vector<int> &comb,int begin,int k, int n) {
        
        if(k==0 && n==0) {
            // vector<int> t(comb);
            combs.push_back(comb);
            return;
        }
        for(int i=begin;i<=9;i++) {
            comb.push_back(i);
            combine(combs,comb,i+1,k-1,n-i);
            comb.pop_back();
        }
    }
    
};