add a simple palindrome solution

Author: xtaci

Makefile

@@ -67,7 +67,8 @@ PROGRAMS =  m_based_demo \
 			sort_demo \
 			bubble_sort_demo \
 			selection_sort_demo	\
-			8queue_demo
+			8queue_demo \
+			palindrome_demo
 
 all: $(PROGRAMS)
 

README.md

@@ -89,6 +89,7 @@
     Knuth–Morris–Pratt algorithm
     Disjoint-Set
 	8-Queue Problem
+	Palindrome
 
 ####贡献者 ( Contributors ) :  
     Samana :  for heavy work of MSVC compatability

include/palindrome.h

@@ -0,0 +1,79 @@
+/*******************************************************************************
+ * DANIEL'S ALGORITHM IMPLEMENTAIONS
+ *
+ *  /\  |  _   _  ._ o _|_ |_  ._ _   _ 
+ * /--\ | (_| (_) |  |  |_ | | | | | _> 
+ *         _|                      
+ *
+ * PALINDROMES
+ *
+ * WORDS LIKE:
+ * 	RACECAR	DEED	LEVEL	PIP
+ * 	ROTOR	CIVIC	POP		MADAM
+ * 	EYE		NUN		RADAR	TOOT
+ * 
+ * This program will find the longest part of mirror.
+ *
+ * http://en.wikipedia.org/wiki/Palindrome
+ ******************************************************************************/
+
+#ifndef _PALINDROME_H_
+#define _PALINDROME_H_
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+namespace alg {
+	static void palindrome(const char * S) {
+		char *R= strdup(S);
+		int len = strlen(S);
+		// reverse
+		for(int i=0;i<len;i++) {
+			R[len-i-1] = S[i];
+		}
+
+		int middle = 0;
+		int maxlen = 0;
+		for(int i=0;i<len;i++) {
+			// compare S[0:i] with R[0:length-i-1] in reverse order
+			int offset = 0;
+			int curlen = 0;
+
+			// try odd
+			while (i-offset>= 0 && len-i-1-offset >= 0) {
+				if (S[i-offset] == R[len-i-1-offset]) {
+					curlen++;
+				} else {
+					break;
+				}
+				offset++;
+			}
+
+			if (curlen > maxlen) {
+				maxlen = curlen;
+				middle = i;
+			}
+
+			// try even
+			while (i-offset>= 0 && len-i-2-offset >= 0) {
+				if (S[i-offset] == R[len-i-2-offset]) {
+					curlen++;
+				} else {
+					break;
+				}
+				offset++;
+			}
+
+			if (curlen > maxlen) {
+				maxlen = curlen;
+				middle = i;
+			}
+		}
+
+		printf("str:%s len:%d middle:%d\n",S, maxlen, middle);
+		free(R);
+	}
+}
+
+#endif //

src/palindrome_demo.cpp

@@ -0,0 +1,8 @@
+#include "palindrome.h"
+#include <stdio.h>
+
+int main() {
+	alg::palindrome("banana");
+	alg::palindrome("abba");
+	alg::palindrome("aaaaa");
+}