Create 39. Combination Sum.cpp

39. Combination Sum.cpp

@@ -0,0 +1,33 @@
+class Solution {
+private:
+    void solve(vector<int>& candidates, int target, int index, vector<int>&temp, vector<vector<int>> &ans)
+    {
+        if(target == 0){
+            ans.push_back(temp);
+            return;
+        }
+        if(target < 0 || index >= candidates.size()){
+            return;
+        }
+
+        //include
+        temp.push_back(candidates[index]);
+        solve(candidates, target-candidates[index], index, temp, ans);
+        //backtrack
+        temp.pop_back();
+
+
+        //exclude
+        solve(candidates, target, index+1, temp, ans);
+
+    } 
+public:
+    vector<vector<int>> combinationSum(vector<int>& candidates, int target) 
+    {
+        vector<vector<int>> ans;
+        vector<int>temp;
+        solve(candidates, target, 0, temp, ans);
+
+        return ans;
+    }
+};