Problem 36

36.c

@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <math.h>
+
+void intToDecimalString (int n, char** string) {
+    *string = malloc (sizeof (char) * (int)(floor (log10 (n)) + 1));
+    sprintf (*string, "%d", n);
+}
+
+void intToBinaryString (int n, char** string) {
+    char hex[9];
+    sprintf (hex, "%x", n);
+
+    char bins[16][5] = { "0000", "0001", "0010", "0011",
+                         "0100", "0101", "0110", "0111",
+                         "1000", "1001", "1010", "1011",
+                         "1100", "1101", "1110", "1111" };
+
+    *string = malloc (sizeof (char) * 33);
+    (*string)[0] = '\0';
+    for (int c = 0; c < 9; c++) {
+        if (hex[c] >= '0' && hex[c] <= '9') {
+            strcat (*string, bins[hex[c] - '0']);
+        }
+        else if (hex[c] >= 'a' && hex[c] <= 'z') {
+            strcat (*string, bins[hex[c] - 'a' + 0xa]);
+        }
+    }
+}
+
+bool isPalindrome (char* string) {
+    int index = 0;
+    while (string[index] == '0')
+        index++;
+
+    bool palindromic = true;
+    int len = strlen (string);
+    for (int i = 0; i < (len - index) / 2; i++) {
+        if (string[index + i] != string[len - i - 1]) {
+            palindromic = false;
+            break;
+        }
+    } 
+
+    return palindromic;
+}
+
+int main () {
+    int sum = 0;
+    for (int i = 1; i < 1000000; i++) {
+        char* decimal;
+        intToDecimalString (i, &decimal);
+        char* binary;
+        intToBinaryString (i, &binary);
+        if (isPalindrome (decimal) && isPalindrome (binary)) {
+            sum += i;
+            printf ("%s, %s\n", decimal, binary);
+        }
+        free (decimal);
+        free (binary);
+    }
+    printf ("%d\n", sum);
+}