Create 39. Combination Sum.md

競技プロ就活部PR用/39. Combination Sum

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+``` python 
+3回目
+# 時間計算量: O(2^N)
+# 空間計算量: O(N)
+N = len(candidates)
+
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+
+        all_valid_combination = []
+
+        def find_vaild_combination(index, current_target, current_combination):
+            if len(candidates) <= index:
+                if  current_target == 0:
+                    all_valid_combination.append(current_combination[:])
+                return
+
+            if  candidates[index] <= current_target:
+                current_combination.append(candidates[index])
+                find_vaild_combination(index, current_target-candidates[index], current_combination)
+                current_combination.pop()
+
+            find_vaild_combination(index+1, current_target, current_combination)
+
+        find_vaild_combination(0, target, [])
+        return all_valid_combination
+```

競技プロ就活部PR用/39.-Combination-Sum 4th.md

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+### 時間: 3m51s
+### Error: 0
+### 時間計算量: O(len(candidates)^(target/min(candidates) + 1))
+### 空間計算量: O(target/min(candidates) + space for Answer)
+```
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        result = []
+        combination = []
+
+        def find_all_combiantions(index, current_target, combination):
+            if index == len(candidates):
+                if current_target == 0:
+                    result.append(combination)
+                return
+
+            if candidates[index] <= current_target:
+                find_all_combiantions(index, current_target - candidates[index], combination + [candidates[index]])
+
+            find_all_combiantions(index + 1, current_target, combination)
+
+        find_all_combiantions(0, target, [])
+        return result
+```