combination-sum.cpp (#63)

Author: prashansatanwar

C++/combination-sum.cpp

@@ -0,0 +1,30 @@
+// Solved using backtracking
+class Solution {
+public:
+    void recur(vector<vector<int>>& ans, vector<int>& v, vector<int>& candidates, int target, int curr){
+        if(target==0){
+            ans.push_back(v);
+        }
+        if(target<0){
+            return; 
+        }
+        for(int i = curr; i< candidates.size(); i++){
+            if(candidates[i]<=target){
+                v.push_back(candidates[i]);
+                recur(ans,v,candidates,target-candidates[i],i);
+                v.pop_back();
+            }
+        }
+    }
+    
+    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
+     vector<vector<int>>ans;
+        vector<int> v;
+        
+        sort(candidates.begin(), candidates.end());
+        
+        recur(ans,v,candidates,target,0);
+        
+        return ans;
+    }
+};

README.md

@@ -270,6 +270,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | --- | ------------------------------------------------------------------- | --------------------------------- | ------------------------- | ----------- | ---------- | ---------------- | ---- |
 | 037 | [Sudoku Solver](https://leetcode.com/problems/sudoku-solver/)       | [C++](./C++/Sudoku-Solver.cpp)    | _O(n^2)_                  | _O(1)_      | Hard       | Hash Table       |      |
 | 980 | [Unique Paths III](https://leetcode.com/problems/unique-paths-iii/) | [C++](./C++/Unique-Paths-III.cpp) | _O(R * C * 2 ^ (R \* C))_ | _O(R \* C)_ | Hard       | DFS, Memoization |      |
+| 39 | [Combination Sum](https://leetcode.com/problems/combination-sum/) | [C++](./C++/combination-sum.cpp) | _O(2^n)_ | _O(n)_ | Medium       | Array, Backtracking |      |
 
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