feat: add solution for smallest palindromic rearrangement ii

- add problem 3518 implementation
- add build configuration with debug and release modes
- add test cases and examples
- add makefile for problem-specific build workflow

3518/README.md

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+# 3518. Smallest Palindromic Rearrangement II
+
+You are given a string `s` and an integer `k`.
+
+Return the k-th palindromic of `s`. If there are fewer than `k` distinct palindromic permutations, return an empty string.
+
+Note: Different rearrangements that yield the same palindromic string are considered identical and are counted once.
+
+## Example 1
+
+**Input:**
+
+```text
+s = "abba", k = 2
+````
+
+**Output:**
+
+```text
+"baab"
+```
+
+**Explanation:**
+
+The two distinct palindromic rearrangements of `"abba"` are `"abba"` and `"baab"`.
+
+Lexicographically, `"abba"` comes before `"baab"`. Since `k = 2`, the output is `"baab"`.
+
+## Example 2
+
+**Input:**
+
+```text
+s = "aa", k = 2
+```
+
+**Output:**
+
+```text
+""
+```
+
+**Explanation:**
+
+There is only one palindromic rearrangement: `"aa"`.
+
+The output is an empty string since `k = 2` exceeds the number of possible rearrangements.
+
+## Example 3
+
+**Input:**
+
+```text
+s = "bacab", k = 1
+```
+
+**Output:**
+
+```text
+"abcba"
+```
+
+**Explanation:**
+
+The two distinct palindromic rearrangements of `"bacab"` are `"abcba"` and `"bacab"`.
+
+Lexicographically, `"abcba"` comes before `"bacab"`. Since `k = 1`, the output is `"abcba"`.
+
+## Constraints
+
+* `1 <= s.length <= 104`
+* `s` consists of lowercase English letters.
+* `s` is guaranteed to be palindromic.
+* `1 <= k <= 106`