diff --git a/combination-sum.py b/combination-sum.py
new file mode 100644
index 00000000..f492eee6
--- /dev/null
+++ b/combination-sum.py
@@ -0,0 +1,96 @@
+#--------Solution 1 : Backtraking------------
+''' Time Complexity : O(2^(m+n)) 
+    Space Complexity : O(m+n) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+'''
+
+class Solution:
+    def __init__(self):
+        self.result = []
+
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        path = []
+        def helper(candidates, i, path, target):
+            #base
+            if i >= len(candidates) or target < 0:
+                return
+            if target == 0:
+                self.result.append(list(path))
+                return
+            #logic
+            #action
+            path.append(candidates[i])
+            #choose
+            helper(candidates, i, path, target-candidates[i])
+            #backtrack
+            path.pop()
+            #no Choose
+            helper(candidates, i+1, path, target)
+        
+        helper(candidates,0,path,target)
+        return self.result
+
+
+#--------Solution 2 : Creating new path each time------------
+''' Time Complexity : O(n*2^(m+n)) 
+    Space Complexity : O(n*h) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+'''
+class Solution:
+    def __init__(self):
+        self.result = []
+
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        path = []
+        def helper(candidates, i, path, target):
+            #base
+            if i >= len(candidates) or target < 0:
+                return
+            if target == 0:
+                self.result.append(list(path))
+                return
+            #logic
+            #action
+            new_p = deepcopy(path)
+            new_p.append(candidates[i])
+            #choose
+            helper(candidates, i, new_p, target-candidates[i])
+            #no Choose
+            helper(candidates, i+1, path, target)
+        
+        helper(candidates,0,path,target)
+        return self.result
+
+#--------Solution 3 : For loop based recursion with backtracking------------
+''' Time Complexity : O(2^(m+n)) 
+    Space Complexity : O(m+n) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+'''
+class Solution:
+    def __init__(self):
+        self.result = []
+
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        path = []
+        def helper(candidates, pivot, path, target):
+            #base
+            if target < 0:
+                return
+            if target == 0:
+                self.result.append(list(path))
+                return
+            #logic
+            #action
+            for i in range(pivot,len(candidates)):
+                path.append(candidates[i])
+                #choose
+                helper(candidates, i, path, target-candidates[i])
+                #backtrack
+                path.pop()
+
+        
+        helper(candidates,0,path,target)
+        return self.result
\ No newline at end of file
diff --git a/expression-add-operator.py b/expression-add-operator.py
new file mode 100644
index 00000000..b3e12a71
--- /dev/null
+++ b/expression-add-operator.py
@@ -0,0 +1,88 @@
+#--------Solution 1 : FOr loop recursion - creating new path for each calll------------
+''' Time Complexity : O(4^n * n) : n for string concatenation at each call
+    Space Complexity : O(n) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+'''
+
+class Solution:
+    def addOperators(self, num: str, target: int) -> List[str]:
+        self.result = []
+        self.target = target
+
+        def helper(num, pivot, calc, tail, path):
+            #base
+            if pivot == len(num):
+                if calc == self.target:
+                    self.result.append(path)
+            #logic
+            for i in range(pivot, len(num)):
+                if num[pivot] == '0' and pivot!=i:
+                    break
+
+                curr = int(num[pivot:i+1])
+                if pivot == 0:
+                    helper(num, i+1, curr, curr, path + str(curr))
+                else:
+                    # for +
+                    helper(num, i+1, calc + curr, curr, path + "+" + str(curr))
+                    #for -
+                    helper(num, i+1, calc - curr, -curr, path + "-" + str(curr))
+                    #for *
+                    helper(num, i+1, calc - tail + (tail * curr) , tail * curr, path + "*" + str(curr))
+            
+        helper(num, 0, 0, 0, "")
+        return self.result
+
+
+#--------Solution 2 : For loop with Backtraking------------
+''' Time Complexity : O(4^n)
+    Space Complexity : O(n) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+'''
+
+class Solution:
+    def addOperators(self, num: str, target: int) -> List[str]:
+        self.result = []
+        self.target = target
+
+        def helper(num, pivot, calc, tail, path):
+            #base
+            if pivot == len(num):
+                if calc == self.target:
+                    self.result.append("".join(path))
+                return
+            #logic
+            for i in range(pivot, len(num)):
+                if num[pivot] == '0' and pivot!=i:
+                    break
+
+                curr = int(num[pivot:i+1])
+                le = len(path)
+                if pivot == 0:
+                    path.append(str(curr))
+                    helper(num, i+1, curr, curr, path)
+                    path.pop()
+                else:
+                    # for +
+                    path.append('+')
+                    path.append(str(curr))
+                    helper(num, i+1, calc + curr, curr, path)
+                    path.pop()
+                    path.pop()
+                    #for -
+                    path.append('-')
+                    path.append(str(curr))
+                    helper(num, i+1, calc - curr, -curr, path)
+                    path.pop()
+                    path.pop()
+                    #for *
+                    path.append('*')
+                    path.append(str(curr))
+                    helper(num, i+1, calc - tail + (tail * curr) , tail * curr, path)
+                    path.pop()
+                    path.pop()
+            
+        helper(num, 0, 0, 0, [])
+        return self.result
\ No newline at end of file