issue #1082: Array: Find first duplicate value in Python

Author: Subham5401

Arrays/find_first_duplicate_value.py

@@ -0,0 +1,26 @@
+'''
+In the code I implemented a solution using Floyd's Tortoise and Hare algorithm 
+for finding the first integer that appears more than once in an array of integers. 
+
+The first solution has a time complexity of O(n) and a space complexity of O(1). 
+It uses the fact that the integers in the array are between 1 and n, inclusive, where n is the length of the array. 
+The solution works by using the array itself as a hash table, 
+by marking an integer as negative if it is encountered for the first time, 
+and returning it if it is already marked negative. 
+
+'''
+
+def find_duplicate(nums):
+    slow = fast = nums[0]
+    while True:
+        slow = nums[slow]
+        fast = nums[nums[fast]]
+        if slow == fast:
+            break
+    
+    slow = nums[0]
+    while slow != fast:
+        slow = nums[slow]
+        fast = nums[fast]
+    
+    return slow