feat(581-shortest-unsorted-continuous-subarray): add py3 solution

0581_shortest-unsorted-continuous-subarray/README.md

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+Given an integer array `nums`, you need to find one **continuous subarray** that if you only sort this subarray in ascending order, then the whole array will be sorted in ascending order.
+
+Return _the shortest such subarray and output its length_.
+
+**Example 1:**
+
+    Input: nums = [2,6,4,8,10,9,15]
+    Output: 5
+    Explanation: You need to sort [6, 4, 8, 10, 9] in ascending order to make the whole array sorted in ascending order.
+    
+
+**Example 2:**
+
+    Input: nums = [1,2,3,4]
+    Output: 0
+    
+
+**Example 3:**
+
+    Input: nums = [1]
+    Output: 0
+    
+
+**Constraints:**
+
+*   `1 <= nums.length <= 104`
+*   `-105 <= nums[i] <= 105`
+
+**Follow up:** Can you solve it in `O(n)` time complexity?

0581_shortest-unsorted-continuous-subarray/python3/solution.py

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+class Solution:
+    def findUnsortedSubarray(self, nums: List[int]) -> int:
+        min_unsorted = float("inf")
+        max_unsorted = float("-inf")
+        
+        # Find min and max element in the unsorted portion
+        for i, num in enumerate(nums):
+            if not self.is_sorted(i, nums):
+                min_unsorted = min(min_unsorted, num)
+                max_unsorted = max(max_unsorted, num)
+        
+        if min_unsorted == float("inf"):
+            return 0
+        
+        # Find right places for min and max elements from previous
+        # step in the "sorted" section of the array
+        left = 0
+        while nums[left] <= min_unsorted:
+            left += 1
+            
+        right = len(nums) - 1
+        while nums[right] >= max_unsorted:
+            right -= 1
+        
+        return right - left + 1
+    
+    def is_sorted(self, i: int, nums: List[int]) -> bool:
+        n = len(nums)
+        
+        if n <= 1:
+            return True
+        
+        if i == 0:
+            return nums[i] <= nums[i + 1]
+        
+        if i == n - 1:
+            return nums[i - 1] <= nums[i]
+        
+        return nums[i - 1] <= nums[i] <= nums[i + 1]