Merge pull request #864 from casnz1601/patch-22

Update 0031.下一个排列.md

problems/0031.下一个排列.md

@@ -120,8 +120,50 @@ class Solution {
 ```
 
 ## Python
-
+>直接使用sorted()不符合题意
 ```python
+class Solution:
+    def nextPermutation(self, nums: List[int]) -> None:
+        """
+        Do not return anything, modify nums in-place instead.
+        """
+        for i in range(len(nums)-1, -1, -1):
+            for j in range(len(nums)-1, i, -1):
+                if nums[j] > nums[i]:
+                    nums[j], nums[i] = nums[i], nums[j]
+                    nums[i+1:len(nums)] = sorted(nums[i+1:len(nums)])
+                    return
+        nums.sort()
+```
+>另一种思路
+```python
+class Solution:
+  '''
+  抛砖引玉：因题目要求“必须原地修改，只允许使用额外常数空间”，python内置sorted函数以及数组切片+sort()无法使用。  
+  故选择另一种算法暂且提供一种python思路
+  '''
+    def nextPermutation(self, nums: List[int]) -> None:
+        """
+        Do not return anything, modify nums in-place instead.
+        """
+        length = len(nums)
+        for i in range(length-1, 0, -1):
+            if nums[i-1] < nums[i]:
+                for j in range(length-1, 0, -1):
+                    if nums[j] > nums[i-1]:
+                        nums[i-1], nums[j] = nums[j], nums[i-1]
+                        break
+                self.reverse(nums, i, length-1)
+                break
+        else:
+            # 若正常结束循环，则对原数组直接翻转
+            self.reverse(nums, 0, length-1)
+
+    def reverse(self, nums: List[int], low: int, high: int) -> None:
+        while low < high:
+            nums[low], nums[high] = nums[high], nums[low]
+            low += 1
+            high -= 1
 ```
 
 ## Go