【Leetcode】【Medium】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 set 2,3,6,7 and target 7, 
A solution set is: 
[7] 
[2, 2, 3]

解题思路：

使用回溯的思想穷举可能的结果。

代码：

 class Solution {
 public:
     vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
         vector<vector<int>> lst;
         vector<int> ans;
         sort(candidates.begin(), candidates.end());
         Backtracking(lst, ans, candidates, , target);
         return lst;
     }

     void Backtracking(vector<vector<int>> &lst, vector<int> ans, vector<int> candidates, int idx, int left) {
         for (int i = idx; i < candidates.size(); ++i) {
             int cur_left = left - candidates[i];
             if (cur_left == ) {
                 ans.push_back(candidates[i]);
                 lst.push_back(ans);
                 return;
             }
             if (cur_left > ) {
                 ans.push_back(candidates[i]);
                 Backtracking(lst, ans, candidates, i, cur_left);
                 ans.pop_back();
             } else {
                 return;
             }
         }
     }
 };

另：是否还有DP/DFS等其他思路。