216. Combination Sum III

题目

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.

样例

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]]

解答

博主对回溯算法不熟，参照了别人做法。

void res(int k, int n, int level, vector<int> &temp, vector<vector<int> > &result) {    cout << "[";    for (auto t : temp)        cout << t << " ";    cout << "]" << endl;    if (n < 0) return;    if (n == 0 && temp.size() == k) result.push_back(temp);    for (int i = level; i <= 9; ++i) {        temp.push_back(i);        res(k, n - i, i + 1, temp, result);        temp.pop_back();    }}vector<vector<int> > combinationSum3(int k, int n) {    vector<vector<int> > result;    vector<int> temp;    res(k, n, 1, temp, result);    return result;}

ps:应该好好学学算法，加油！