Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -357,6 +357,7 @@ _**Note:** Our group is currently taking a break from grinding leetcode. The tab
 | June 9, 2025 | [440](https://leetcode.com/problems/k-th-smallest-in-lexicographical-order/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/440) | 🔴 Hard |
 | June 10, 2025 | [3442](https://leetcode.com/problems/maximum-difference-between-even-and-odd-frequency-i/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3442) | 🟢 Easy |
 | June 11, 2025 | [3445](https://leetcode.com/problems/maximum-difference-between-even-and-odd-frequency-ii/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3445) | 🔴 Hard |
+| June 12, 2025 | [3423](https://leetcode.com/problems/maximum-difference-between-adjacent-elements-in-a-circular-array/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3423) | 🟢 Easy |
 
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