From 3b71bbbca8b4aecc10fb1b3e26639bf31f010a42 Mon Sep 17 00:00:00 2001
From: Ivan Reshetnikov <ordinarydev@protonmail.com>
Date: Sat, 19 Nov 2022 17:43:23 +0500
Subject: [PATCH] Problem 9: palindrome number

---
 problems/9-palindrome-number/Makefile |  1 +
 problems/9-palindrome-number/lib.c    | 32 +++++++++++++++++++++++++++
 problems/9-palindrome-number/lib.h    |  4 ++++
 problems/9-palindrome-number/main.c   | 18 +++++++++++++++
 4 files changed, 55 insertions(+)
 create mode 120000 problems/9-palindrome-number/Makefile
 create mode 100644 problems/9-palindrome-number/lib.c
 create mode 100644 problems/9-palindrome-number/lib.h
 create mode 100644 problems/9-palindrome-number/main.c

diff --git a/problems/9-palindrome-number/Makefile b/problems/9-palindrome-number/Makefile
new file mode 120000
index 0000000..25eaf27
--- /dev/null
+++ b/problems/9-palindrome-number/Makefile
@@ -0,0 +1 @@
+../template/Makefile
\ No newline at end of file
diff --git a/problems/9-palindrome-number/lib.c b/problems/9-palindrome-number/lib.c
new file mode 100644
index 0000000..7fea0bd
--- /dev/null
+++ b/problems/9-palindrome-number/lib.c
@@ -0,0 +1,32 @@
+#include "lib.h"
+
+bool isPalindrome(int x) {
+    if (x < 0)
+        return false;
+
+    // Find length and calculate divisor
+    int len = 0;
+    int div = 1;
+    int copy = x;
+    while (copy > 0) {
+        copy /= 10;
+        if (len != 0)
+            div *= 10;
+        len++;
+    }
+
+    // Compare digits
+    for (int i=0; i<len/2; i++) {
+        int a = x / div;
+        int b = x % 10;
+        if (a != b)
+            return false;
+        
+        // Remove first and last digit
+        x = x % div;
+        x /= 10;
+        div /= 100;
+    }
+
+    return true;
+}
diff --git a/problems/9-palindrome-number/lib.h b/problems/9-palindrome-number/lib.h
new file mode 100644
index 0000000..24d1900
--- /dev/null
+++ b/problems/9-palindrome-number/lib.h
@@ -0,0 +1,4 @@
+#pragma once
+#include <stdbool.h>
+
+bool isPalindrome(int x);
diff --git a/problems/9-palindrome-number/main.c b/problems/9-palindrome-number/main.c
new file mode 100644
index 0000000..37d3532
--- /dev/null
+++ b/problems/9-palindrome-number/main.c
@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include "lib.h"
+
+int main() {
+    int a = 121;
+    printf("Test 1: %d\n", isPalindrome(a) == 1);
+
+    int b = -121;
+    printf("Test 2: %d\n", isPalindrome(b) == 0);
+
+    int c = 1234554321;
+    printf("Test 3: %d\n", isPalindrome(c) == 1);
+
+    int d = 2147483647;
+    printf("Test 4: %d\n", isPalindrome(d) == 0);
+
+    return 0;
+}