add contains-duplicate py3 soln

0217_contains-duplicate/README.md

@@ -0,0 +1,24 @@
+Given an integer array `nums`, return `true` if any value appears **at least twice** in the array, and return `false` if every element is distinct.
+
+**Example 1:**
+
+    Input: nums = [1,2,3,1]
+    Output: true
+    
+
+**Example 2:**
+
+    Input: nums = [1,2,3,4]
+    Output: false
+    
+
+**Example 3:**
+
+    Input: nums = [1,1,1,3,3,4,3,2,4,2]
+    Output: true
+    
+
+**Constraints:**
+
+*   `1 <= nums.length <= 105`
+*   `-109 <= nums[i] <= 109`

0217_contains-duplicate/python3/solution.py

@@ -0,0 +1,11 @@
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        counts = {}
+        
+        for num in nums:
+            counts[num] = counts.get(num, 0) + 1
+            
+            if counts[num] > 1:
+                return True
+        
+        return False