Create 2024-07-27-217-Contains-Duplicate.md

Author: nguyentp

_posts/2024-07-27-217-Contains-Duplicate.md

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+---
+title: 217. Contains Duplicate
+author: nguyentp
+date: 2024-07-27
+tags: [leetcode]
+render_with_liquid: false
+---
+
+# [Problem understanding](https://leetcode.com/problems/contains-duplicate/)
+
+```
+Input: nums = [1,2,3,1]
+Output: true
+```
+
+- 1 appears twice -> return True.
+- Base on the constraint, number could be negative or zero.
+
+# Edge case
+
+- empty list: False
+- single element: False
+- `[1, 1, 1, 1]` input: True
+
+# Solution
+
+1. 2 nested loop. Time N^2, Space N.
+2. Hash: `seen` hash table to check whether we have seen a number. Then go through each number, if we see it the first time, put it into the `seen` hash table. Otherwise, there is duplicate. Time: N, Space: N.
+
+# Implement
+
+```
+class Solution(object):
+    def containsDuplicate(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: bool
+        """
+        if len(nums) <= 1:
+            return False
+        
+        seen = set()
+        for n in nums:
+            if n in seen:
+                return True
+            seen.add(n)
+        return False
+```