Add 287 find theduplicate number Solution in python

Algorithms/Medium/287_FindTheDuplicateNumber/Solution.py

@@ -0,0 +1,25 @@
+from typing import List
+
+class Solution:
+    def _get_count_of_equal_or_less(self, num_arr: List[int], value: int) -> int:
+        return len([num for num in num_arr if num <= value])
+
+    def findDuplicate(self, nums: List[int]) -> int:        
+        left = 1
+        right = len(nums) - 1
+
+        duplicate_number = -1
+
+        while left <= right:
+            mid = (left + right)//2
+
+            equal_or_less_count = self._get_count_of_equal_or_less(num_arr=nums, value=mid)
+
+            if equal_or_less_count > mid:
+                right = mid - 1
+                duplicate_number = mid
+            else:
+                left = mid + 1                    
+
+        return duplicate_number
+