Update 0031.下一个排列.md

python版本剪枝去重，避免对递减序列的比较

problems/0031.下一个排列.md

@@ -168,7 +168,8 @@ class Solution:
         Do not return anything, modify nums in-place instead.
         """
         length = len(nums)
-        for i in range(length - 1, -1, -1):
+        for i in range(length - 2, -1, -1): # 从倒数第二个开始
+            if nums[i]>=nums[i+1]: continue # 剪枝去重
             for j in range(length - 1, i, -1):
                 if nums[j] > nums[i]:
                     nums[j], nums[i] = nums[i], nums[j]