Combination Sum Problem


Description

LeetCode Problem 39.

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:

1
2
3
4
5
6
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:

1
2
Input: candidates = [2,3,5], target = 8
Output: [[2,2,2,2],[2,3,3],[3,5]]

Example 3:

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

Example 4:

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

Example 5:

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

Constraints:

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


Sample C++ Code

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
class Solution {
public:
    vector<vector<int>> ans;
    
    void dfs(vector<int>& candidates, vector<int>& comb, int target, int idx) {
        if (target == 0) {
            ans.push_back(comb);
        }
        if (target <= 0)
            return;
        
        for (int i = idx; i < candidates.size(); i ++) {
            if (candidates[i] <= target) {
                comb.push_back(candidates[i]);
                dfs(candidates, comb, target-candidates[i], i);
                comb.pop_back();
            }
        }
        return;
    }
    
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<int> comb;
        sort(candidates.begin(), candidates.end());
        dfs(candidates, comb, target, 0);
        return ans;
    }
};




Related Posts

Unique Paths III Problem

LeetCode 980. You are given an m x n integer...

Split Array Into Fibonacci Sequence Problem

LeetCode 842. You are given a string of digits num,...

Partition To K Equal Sum Subsets Problem

LeetCode 698. Given an integer array nums and an integer...

Letter Case Permutation Problem

LeetCode 784. Given a string s, we can transform every...

24 Game Problem

LeetCode 679. You are given an integer array cards of...

Matchsticks To Square Problem

LeetCode 473. You are given an integer array matchsticks where...