feat(math): add palindrome number checker using standard headers

math/palindrome_number.cpp

@@ -0,0 +1,47 @@
+/**
+ * @file
+ * @brief Check if a given number is a palindrome
+ * @details
+ * This program defines a function `is_palindrome_number()` which checks whether
+ * a number reads the same backward as forward.
+ * Negative numbers are treated as non-palindromic.
+ *
+ * @see https://en.wikipedia.org/wiki/Palindrome
+ */
+
+#include <iostream>
+#include <string>
+#include <vector>
+
+/**
+ * @brief Checks if an integer is a palindrome number.
+ * @param n The number to check.
+ * @return `true` if `n` is a palindrome, otherwise `false`.
+ */
+bool is_palindrome_number(long long n) {
+    if (n < 0)
+        return false;
+    std::string s = std::to_string(n);
+    int i = 0, j = static_cast<int>(s.size()) - 1;
+    while (i < j) {
+        if (s[i] != s[j])
+            return false;
+        ++i;
+        --j;
+    }
+    return true;
+}
+
+#ifdef RUN_LOCAL
+/**
+ * @brief Example test cases for the palindrome number checker.
+ */
+int main() {
+    std::vector<long long> tests = {121, -121, 10, 12321, 0};
+    for (auto t : tests) {
+        std::cout << t << " -> " << (is_palindrome_number(t) ? "True" : "False")
+                  << "\n";
+    }
+    return 0;
+}
+#endif