Add solution for Combination Sum problem

Author: jamiebase

combination-sum/gcount85.py

@@ -0,0 +1,37 @@
+"""
+# Intuition
+backtracking
+
+# Complexity
+- Time complexity: N을 깊이만큼 곱한다. 따라서 아래와 같을 때, O(N^(T/M))
+    N = candidates 개수
+    T = target
+    M = candidates 중 최소값
+
+- Space complexity: O(T/M)
+"""
+
+
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        candidates.sort()
+        answer = []
+        output = []
+
+        def dfs(cur_i, cur_sum):
+            if cur_sum == target:
+                answer.append(output[:])
+                return
+
+            for i in range(cur_i, len(candidates)):
+                num = candidates[i]
+
+                if cur_sum + num > target:
+                    break
+
+                output.append(num)
+                dfs(i, cur_sum + num)
+                output.pop()
+
+        dfs(0, 0)
+        return answer