Valid palindrome

Signed-off-by: begeekmyfriend <[email protected]>

125_valid_palindrome/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test valid_palindrome.c

125_valid_palindrome/valid_palindrome.c

@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+static bool valid(char c)
+{
+    return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
+}
+
+bool isPalindrome(char* s)
+{
+    int len = strlen(s);
+    int low = 0;
+    int high = len - 1;
+
+    while (low < high) {
+        if (!valid(s[low])) {
+            low++;
+        } else if (!valid(s[high])) {
+            high--;
+        } else if (s[low] == s[high]) {
+            low++;
+            high--;
+        } else {
+            if (isalpha(s[low]) && isalpha(s[high])) {
+                int diff = s[low] > s[high] ? s[low] - s[high] : s[high] - s[low];
+                if (diff == 'a' - 'A') {
+                    low++;
+                    high--;
+                } else {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        }
+    }
+
+    return low >= high;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "Usage: ./test string\n");
+        exit(-1);
+    }
+    printf("%s\n", isPalindrome(argv[1]) ? "true" : "false");
+    return 0;
+}