Day-56 Dynamic programming problems 2

Author: mandliya

README.md

@@ -6,7 +6,7 @@
 | :------------: | :----------: |
 | Total Problems | 77 |
 | Current Streak | 55 |
-| Longest Streak | 55 ( August 17, 2015 - October 10, 2015 ) |
+| Longest Streak | 55 ( August 17, 2015 - October 12, 2015 ) |
 
 </center>
 

string_problems/z.cpp

@@ -0,0 +1,66 @@
+#include <iostream>
+#include <string>
+#include <vector>
+
+
+/**
+ * Function to fill in zvalues vector of ztext
+ */
+std::vector<size_t> fillZvalues(const std::string & ztext) {
+	size_t n = ztext.length();
+	std::vector<size_t> zvals(n, 0);
+	size_t L = 0, R = 0; 								// s[L..R] represent the prefix string.
+	for (size_t i = 1; i < n; ++i) {
+		if ( i > R ) {
+			L = R = i;
+			while( R < n && ztext[R-L] == ztext[R] ) {
+				++R;
+			}
+			zvals[i] = R-L;
+			--R;
+		} else {
+			size_t K = i - L;
+			if( zvals[K] < R-i+1 ) {
+				zvals[i] = zvals[K];
+			} else {
+				L = R = i;
+				while( R < n && ztext[R-L] == ztext[R] ) {
+					++R;
+				}
+				zvals[i] = R-L;
+				--R;
+			}
+		}
+	}
+	return zvals;
+}
+
+/**
+ * This function returns index of text where pattern matches using z algorithm
+ */
+std::vector<size_t> search( const std::string & text, const std::string & pattern ) {
+	std::string ztext = pattern + '$' + text;
+	std::vector<size_t> zvalues = fillZvalues(ztext);
+	std::vector<size_t> indices;
+	for ( size_t i = 1; i < zvalues.size(); ++i ) {
+		if (zvalues[i] == pattern.length()) {
+			indices.push_back(i - pattern.length() -1 );
+		}
+	}
+	return indices;
+}
+
+int main()
+{
+	std::string text, pattern;
+	std::cout << "String searching using Z algorithm:\n";
+	std::cout << "Enter text:";
+	std::getline(std::cin, text);
+	std::cout << "Pattern :";
+	std::getline(std::cin, pattern);
+	std::vector<size_t> indices = search(text, pattern);
+	for (auto i : indices ) {
+		std::cout << pattern << " occurs in given text starting at index " << i << std::endl;
+	}
+	return 0;
+}