diff --git a/combination-sum.py b/combination-sum.py
new file mode 100644
index 00000000..4942c88c
--- /dev/null
+++ b/combination-sum.py
@@ -0,0 +1,21 @@
+# Time Complexity : O(N^target)
+# Space Complexity : O(target)
+# Did this code successfully run on Leetcode : Yes
+# Any problem you faced while coding this : No
+
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        res = []
+        def backtrack(remain, comb, start):
+            if remain == 0:
+                res.append(list(comb))
+                return
+            elif remain < 0:
+                return
+            for i in range(start, len(candidates)):
+                comb.append(candidates[i])
+                backtrack(remain - candidates[i], comb, i)
+                comb.pop()
+        backtrack(target, [], 0)
+        return res
+        
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diff --git a/expression-add-operators.py b/expression-add-operators.py
new file mode 100644
index 00000000..f8f1f46e
--- /dev/null
+++ b/expression-add-operators.py
@@ -0,0 +1,30 @@
+# 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]:
+        res = []
+        n = len(num)
+        
+        def backtrack(index, path, value, prev):
+            if index == n:
+                if value == target:
+                    res.append(path)
+                return
+            for i in range(index, n):
+                # Avoid numbers with leading zeros
+                if i != index and num[index] == '0':
+                    break
+                curr_str = num[index:i+1]
+                curr = int(curr_str)
+                if index == 0:
+                    backtrack(i+1, curr_str, curr, curr)
+                else:
+                    backtrack(i+1, path + '+' + curr_str, value + curr, curr)
+                    backtrack(i+1, path + '-' + curr_str, value - curr, -curr)
+                    backtrack(i+1, path + '*' + curr_str, value - prev + prev * curr, prev * curr)
+        backtrack(0, '', 0, 0)
+        return res
+        
\ No newline at end of file