Added solution for "287. Find the Duplicate Number ".

Author: Meuman

leetcode/python/find.duplicate.number.py

@@ -0,0 +1,19 @@
+class Solution:
+    def findDuplicate(self, nums: List[int]) -> int:
+        tortoise = nums[0]
+        hare = nums[0]
+        # do {
+        #     tortoise = nums[tortoise]
+        #     hare = nums[nums[hare]]
+        # } while (tortoise != hare)
+        while 1:
+            tortoise = nums[tortoise]
+            hare = nums[nums[hare]]
+            if tortoise==hare:
+                break
+        ptr1 = nums[0]
+        ptr2 = hare
+        while (ptr1 != ptr2):
+            ptr1 = nums[ptr1]
+            ptr2 = nums[ptr2]
+        return ptr1;