Initial commit of palindromefinder

2 files changed, 142 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..110957b
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,6 @@
+out = palindromfinder
+cc = cc
+
+all:
+	$(cc) -O3 src/main.c -o $(out)
+
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..7bdaba0
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,136 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+//
+// Compare the whole thing by passing 0 as end
+//
+// @param str String to check for palindrome
+// @param end For checking a substring shorter than the end of str
+//
+// @return int Is a palindrome (1) or not (0)
+//
+char is_palindrome(char* str, long len) {
+  //long len;
+  long i = 0;
+  long n = len;
+
+  // This handles comparisons of odd and even length strings
+  while(n - i > 0) {
+    if(str[i] == str[n]) {
+      i++;
+      n--;
+    } else {
+      return 0;
+    }
+  }
+  return 1;
+}
+
+
+//
+// Finds the largest palindrome in a data set
+//
+// @param data Data chunk to search for the largest palindrome
+//
+void find_largest_palindromes(char* data) {
+  int largest_start = 0;
+  int largest_end = 0;
+  int largest_len = 0;
+
+  // get length
+  int len = 0;
+  while(data[len] != '\0')
+    len++;
+
+  int start;
+  int end = len;
+  int palindrome;
+  while(end > 0) {
+    // Moving the start index
+    start = 0;
+    while(start < (end - largest_len)) {
+      //printf("testing s: %d  e: %d\n", start, end);
+      // Moving the end index
+
+      //printf("%.*s\n", end - start, &data[start]);
+      palindrome = is_palindrome(&data[start], end - start);
+      if(palindrome == 1) {
+        // Update the largest if this one is bigger
+        int curlen = end - start;
+        if(curlen > largest_len) {
+          largest_len = curlen;
+          largest_start = start;
+          largest_end = end;
+          printf("Found new largest: %d chars long\n", largest_len + 1);
+          break;
+        }
+      }
+      start++;
+    }
+    end--;
+  }
+  printf("Longest palindrome is %d long\n", largest_len + 1);
+  printf("It starts at %d and ends at %d\n", largest_start, largest_end);
+  printf("Value: %.*s\n", largest_end - largest_start + 1, &data[largest_start]);
+}
+
+
+//
+// Function for testing one-off strings
+// Useful for debugging
+//
+// @param str String to test for palindromeism
+//
+void palstr(char* str) {
+   if(is_palindrome(str, 0) == 1) {
+     printf("%s \e[1mis\e[0m a palindrome!\n", str);
+   } else {
+     printf("%s is \e[1mnot\e[0m a palindrome.\n", str);
+   }
+}
+
+
+//
+// Ye olde' main function
+//
+int main(int argc, char *argv[]) {
+  if(argc < 2) {
+    printf("Please specify a string to check for palindrome-ism.\n");
+    return 1;
+  }
+
+  FILE *f = fopen(argv[1], "r");
+
+  // If the file can't be opened, try using the passed value as a palindrome
+  // test
+  if(!f) {
+    palstr(argv[1]);
+    return 0;
+  }
+  
+  printf("Scanning file %s\n", argv[1]);
+  // Get file length
+  unsigned int flen = 0;
+  while(fgetc(f) != EOF) {
+    flen++;
+  }
+
+  rewind(f);
+
+  printf("Allocating memory\n");
+  // Allocate array for file contents
+  char data[flen + 1];
+  int i = 0;
+  char c;
+  printf("Reading data to memory\n");
+  while((c = fgetc(f)) != EOF) {
+    data[i] = c;
+    i++;
+  }
+  
+  fclose(f);
+
+  printf("Searching for palindromes\n");
+  find_largest_palindromes(data);
+  return 0;
+}