Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -486,6 +486,7 @@ _**Note:** Our group is currently taking a break from grinding leetcode. The tab
 | October 16, 2025 | [2598](https://leetcode.com/problems/smallest-missing-non-negative-integer-after-operations/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/2598) | 🟡 Medium |
 | October 17, 2025 | [3003](https://leetcode.com/problems/maximize-the-number-of-partitions-after-operations/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3003) | 🔴 Hard |
 | October 18, 2025 | [3397](https://leetcode.com/problems/maximum-number-of-distinct-elements-after-operations/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3397) | 🟡 Medium |
+| October 19, 2025 | [1625](https://leetcode.com/problems/lexicographically-smallest-string-after-applying-operations/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1625) | 🟡 Medium |
 
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