chore: clean up content phase organization

apps/docs/content/(01-linear-structures)/hash-table/217-contains-duplicate.mdx

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+---
+title: '217. Contains Duplicate'
+description: 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
+sidebar:
+  label: 'Contains Duplicate'
+  badge: 'Easy'
+---
+
+<Badge variant="accent">Array</Badge>
+
+### Example 1:
+- Input: `nums = [1,2,3,1]`
+- Output: `true`
+- Explanation: The element `1` occurs at the indices `0` and `3`.
+
+### Example 2:
+- Input: `nums = [1,2,3,4]`
+- Output: `false`
+- Explanation: All elements are distinct.
+
+### Example 3:
+- Input: `nums = [1,1,1,3,3,4,3,2,4,2]`
+- Output: `true`
+
+### Constraints:
+
+- `1 <= nums.length <= 10^5`
+- `-10^9 <= nums[i] <= 10^9`
+
+## Approach
+
+```mermaid
+flowchart TD
+  S(["containsDuplicate(nums)"]) --> I["freq = {}"]
+  I --> L{"more n in nums?"}
+  L -- no --> E(["return false"])
+  L -- yes --> C["freq[n] = (freq[n] or 0) + 1"]
+  C --> Q{"freq[n] >= 2?"}
+  Q -- yes --> R(["return true"])
+  Q -- no --> L
+```
+
+## Solution
+
+```py
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        return len(set(nums)) != len(nums)
+```
+
+## Explanation
+
+<YouTube id="3OamzN90kPg" title="Contains Duplicate - Leetcode 217 - Python" />