LeetCode Combination Sum

LeetCode Combination Sum

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

The same repeated number may be chosen from C unlimited number of times.

Note:

• All numbers (including target) will be positive integers.
• Elements in a combination (a1, a2 ,... , Ak) must be in non-descending order. (ie, a1 ≤ a2 ≤... ≤ Ak ).
• The solution set must not contain duplicate combinations.

  For example, given candidate set2,3,6,7And target7,
  A solution set is:
  [7]
[2, 2, 3]

  Find the combination of sum and target from the array. Each number can be repeated.

  Idea: after sorting, we use backtracking. In order to ensure that each number can be repeated, we can start from the subscript of this number during enumeration.

  class Solution {public:    void dfs(vector
     
       candidates, int index, int sum, int target, vector
      
       > &res, vector
       
         &path) {        if (sum > target) return;        if (sum == target) {            res.push_back(path);            return;        }        for (int i = index; i < candidates.size(); i++) {            path.push_back(candidates[i]);            dfs(candidates, i, sum+candidates[i], target, res, path);            path.pop_back();        }    }    vector
        
          > combinationSum(vector
         
           &candidates, int target) {        sort(candidates.begin(), candidates.end());        vector
          
            > res; vector
           
             path; dfs(candidates, 0, 0, target, res, path); return res; }};