feat: added z_algorithm in strings

DIRECTORY.md

@@ -333,3 +333,4 @@
  * [Knuth Morris Pratt](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/strings/knuth_morris_pratt.cpp)
  * [Manacher Algorithm](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/strings/manacher_algorithm.cpp)
  * [Rabin Karp](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/strings/rabin_karp.cpp)
+ * [Z Function](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/strings/z_function.cpp)

strings/z_function.cpp

@@ -0,0 +1,96 @@
+/**
+ * @file
+ * @brief The [Z function](https://cp-algorithms.com/string/z-function.html) for
+ * finding occurences of a pattern within a piece of text with time and space
+ * complexity O(n + m)
+ * @details
+ * 1. The Z-function for a string is an array of length n where the
+ * i-th element is equal to the greatest number of characters starting
+ * from the position i that coincide with the first characters of s.
+ * 2. E.g.: string: ababb then z[2]=2 as s[2]=s[0] and s[3]=s[1] and s[4]!=s[2]
+ * @author [Ritika Gupta](https://github.com/RitikaGupta8734)
+ */
+
+#include <iostream> /// for IO operations
+#ifdef _MSC_VER
+#include <string> /// for string (use this for MS Visual C++)
+#else
+#include <cstring> /// for string
+#endif
+#include <cassert> /// for assert
+#include <vector> /// for std::vector
+
+/**
+ * @brief Generate the Z-function for the inputted string.
+ * \param[in] pattern text on which to apply the Z-function
+ * \returns the Z-function output as a vector array
+ */
+std::vector<uint64_t> Z_function(const std::string &pattern) {
+ uint64_t pattern_length = pattern.size();
+ std::vector<uint64_t> z(pattern_length, 0);
+
+ for (uint64_t i = 1, l = 0, r = 0; i < pattern_length; i++) {
+ if (i <= r) {
+ z[i] = std::min(r - i + 1, z[i - l]);
+ }
+ while (i + z[i] < pattern_length &&
+ pattern[z[i]] == pattern[i + z[i]]) {
+ z[i]++;
+ }
+ if (i + z[i] - 1 > r) {
+ r = i + z[i] - 1;
+ }
+ }
+ return z;
+}
+
+/**
+ * @brief Using Z_function to find a pattern in a text
+ * \param[in] pattern string pattern to search
+ * \param[in] text text in which to search
+ * \returns a vector of starting indexes where pattern is found in the text
+ */
+std::vector<uint64_t> find_pat_in_text(const std::string &pattern,
+ const std::string &text) {
+ uint64_t text_length = text.size(), pattern_length = pattern.size();
+ std::vector<uint64_t> z = Z_function(pattern + '#' + text);
+ std::vector<uint64_t> matching_indexes;
+
+ for (uint64_t i = 0; i < text_length; i++) {
+ if (z[i + pattern_length + 1] == pattern_length) {
+ matching_indexes.push_back(i);
+ }
+ }
+ return matching_indexes;
+}
+
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void test() {
+ // usual case
+ std::string text1 = "alskfjaldsabc1abc1abcbksbcdnsdabcabc";
+ std::string pattern1 = "abc";
+
+ // matching_indexes1 gets the indexes where pattern1 exists in text1
+ std::vector<uint64_t> matching_indexes1 = find_pat_in_text(pattern1, text1);
+ assert((matching_indexes1 == std::vector<uint64_t>{10, 14, 18, 30, 33}));
+
+ // corner case
+ std::string text2 = "greengrass";
+ std::string pattern2 = "abc";
+
+ // matching_indexes2 gets the indexes where pattern2 exists in text2
+ std::vector<uint64_t> matching_indexes2 = find_pat_in_text(pattern2, text2);
+ assert((matching_indexes2 == std::vector<uint64_t>{}));
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+ test(); // run self-test implementations
+ return 0;
+}