Combination Sum

Author: Shikha-code36

Backtracking/39-Combination-Sum.py

@@ -0,0 +1,39 @@
+''' Leetcode- https://leetcode.com/problems/combination-sum/'''
+'''
+Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order.
+
+The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different.
+
+It is guaranteed that the number of unique combinations that sum up to target is less than 150 combinations for the given input.
+
+Example 1:
+
+Input: candidates = [2,3,6,7], target = 7
+Output: [[2,2,3],[7]]
+Explanation:
+2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.
+7 is a candidate, and 7 = 7.
+These are the only two combinations.
+'''
+
+
+def combinationSum(candidates, target):
+    res = []
+
+    def dfs(i, cur, total):
+        if total == target:
+            res.append(cur.copy())
+            return
+        if i >= len(candidates) or total > target:
+            return
+
+        cur.append(candidates[i])
+        dfs(i, cur, total+candidates[i])
+        cur.pop()
+        dfs(i+1, cur, total)
+
+    dfs(0, [], 0)
+    return res
+
+#T: O(2^T)
+#S: O(N)

README.md

@@ -13,4 +13,5 @@ Check the notes for the explaination - [Notes](https://stingy-shallot-4ea.notion
     - [x] [Permutations](Backtracking/46-Permutations.py)
     - [x] [Permutations II](Backtracking/47-Permutations-II.py)
     - [x] [Combinations](Backtracking/77-Combinations.py)
+    - [x] [Combination Sum](Backtracking/39-Combination-Sum.py)