Merge pull request #250 from jojoo15/patch-24

添加 0039.组合总数 python3版本

problems/0039.组合总和.md

@@ -271,8 +271,25 @@ class Solution {
 ```
 
 Python：
-
+```python3
-
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        res = []
+        path = []
+        def backtrack(candidates,target,sum,startIndex):
+            if sum > target: return 
+            if sum == target: return res.append(path[:])
+            for i in range(startIndex,len(candidates)):
+                if sum + candidates[i] >target: return  #如果 sum + candidates[i] > target 就终止遍历
+                sum += candidates[i] 
+                path.append(candidates[i])
+                backtrack(candidates,target,sum,i)  #startIndex = i:表示可以重复读取当前的数
+                sum -= candidates[i]  #回溯
+                path.pop()  #回溯
+        candidates = sorted(candidates)  #需要排序
+        backtrack(candidates,target,0,0)
+        return res
+```
 Go：