Today I have done leetcode's February LeetCoding Challenge with cpp.

February LeetCoding Challenge 17

Description

Combination Sum

Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order.

The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different.

It is guaranteed that the number of unique combinations that sum up to target is less than 150 combinations for the given input.

Example 1:

Input: candidates = [2,3,6,7], target = 7
Output: [[2,2,3],[7]]
Explanation:
2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.
7 is a candidate, and 7 = 7.
These are the only two combinations.

Example 2:

Input: candidates = [2,3,5], target = 8
Output: [[2,2,2,2],[2,3,3],[3,5]]

Example 3:

Input: candidates = [2], target = 1
Output: []

Constraints:

• 1 <= candidates.length <= 30
• 1 <= candidates[i] <= 200
• All elements of candidates are distinct.
• 1 <= target <= 500

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
  void solve(
    vector<vector<int>> &answer,
    vector<int> &tmp,
    vector<int> &candidates,
    int index,
    int rest
  ) {
    if(!rest) {
      answer.push_back(tmp);
      return;
    }
    if(index == candidates.size()) return;
    int curSize = tmp.size();
    while(rest >= 0) {
      solve(answer, tmp, candidates, index + 1, rest);
      rest -= candidates[index];
      tmp.push_back(candidates[index]);
    }
    while(curSize < tmp.size()) tmp.pop_back();
  }
public:
  vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
    vector<vector<int>> answer;
    vector<int> tmp;
    solve(answer, tmp, candidates, 0, target);
    return answer;
  }
};

// Accepted
// 170/170 cases passed (6 ms)
// Your runtime beats 80.84 % of cpp submissions
// Your memory usage beats 46.83 % of cpp submissions (11.2 MB)