documented kmp string search

strings/knuth_morris_pratt.cpp

@@ -1,64 +1,88 @@
-/*
-    The Knuth-Morris-Pratt Algorithm for finding a pattern within a piece of text
-    with complexity O(n + m)
-    1) Preprocess pattern to identify any suffixes that are identical to prefixes
-        This tells us where to continue from if we get a mismatch between a character in our pattern
-        and the text.
-    2) Step through the text one character at a time and compare it to a character in the pattern
-        updating our location within the pattern if necessary
-*/
+/**
+ * \file
+ * \brief The [Knuth-Morris-Pratt
+ * Algorithm](https://en.wikipedia.org/wiki/Knuth–Morris–Pratt_algorithm) for
+ * finding a pattern within a piece of text with complexity O(n + m)
+ *
+ * 1. Preprocess pattern to identify any suffixes that are identical to
+ * prefixes. This tells us where to continue from if we get a mismatch between a
+ * character in our pattern and the text.
+ * 2. Step through the text one character at a time and compare it to a
+ * character in the pattern updating our location within the pattern if
+ * necessary
+ */
 
-#include<iostream>
-#include<vector>
-#include<string>
-using namespace std;
-vector<int> getFailureArray(string pattern){
-    int pattern_length=pattern.size();
-    vector<int>failure(pattern_length+1);
-    failure[0]=-1;
-    int j=-1;
-    for(int i=0; i<pattern_length; i++){
-        while(j!=-1&&pattern[j]!=pattern[i]){
-            j=failure[j];
+#include <iostream>
+#ifdef _MSC_VER
+#include <string>  // use this for MS Visucal C++
+#else
+#include <cstring>
+#endif
+#include <vector>
+
+/**
+ * Generate the partial match table aka failure function for a pattern to
+ * search.
+ * \param[in] pattern text for which to create the partial match table
+ * \returns the partial match table as a vector array
+ */
+std::vector<int> getFailureArray(const std::string &pattern) {
+    int pattern_length = pattern.size();
+    std::vector<int> failure(pattern_length + 1);
+    failure[0] = -1;
+    int j = -1;
+
+    for (int i = 0; i < pattern_length; i++) {
+        while (j != -1 && pattern[j] != pattern[i]) {
+            j = failure[j];
         }
         j++;
-        failure[i+1]=j;
+        failure[i + 1] = j;
     }
     return failure;
 }
-bool kmp(string pattern,string text){
-    int text_length=text.size(),pattern_length=pattern.size();
-    vector<int>failure=getFailureArray(pattern);
-    int k=0;
-    for(int  j=0; j<text_length; j++){
-        while(k!=-1&&pattern[k]!=text[j]){
-            k=failure[k];
+
+/**
+ * KMP algorithm to find a pattern in a text
+ * \param[in] pattern string pattern to search
+ * \param[in] text text in which to search
+ * \returns `true` if pattern was found
+ * \returns `false` if pattern was not found
+ */
+bool kmp(const std::string &pattern, const std::string &text) {
+    int text_length = text.size(), pattern_length = pattern.size();
+    std::vector<int> failure = getFailureArray(pattern);
+
+    int k = 0;
+    for (int j = 0; j < text_length; j++) {
+        while (k != -1 && pattern[k] != text[j]) {
+            k = failure[k];
         }
         k++;
-        if(k==pattern_length)return true;
+        if (k == pattern_length)
+            return true;
     }
     return false;
 }
 
-int main()
-{   
-   
-    string text="alskfjaldsabc1abc1abc12k23adsfabcabc";
-    string pattern="abc1abc12l";
-    if(kmp(pattern,text)==true){
-        cout<<"Found"<<endl;
+/** Main function */
+int main() {
+    std::string text = "alskfjaldsabc1abc1abc12k23adsfabcabc";
+    std::string pattern = "abc1abc12l";
+
+    if (kmp(pattern, text) == true) {
+        std::cout << "Found" << std::endl;
+    } else {
+        std::cout << "Not Found" << std::endl;
     }
-    else{
-        cout<<"Not Found"<<endl;
-    }
-    text="abcabc";
-    pattern="bca";
-    if(kmp(pattern,text)==true){
-        cout<<"Found"<<endl;
-    }
-    else{
-        cout<<"Not Found"<<endl;
+
+    text = "abcabc";
+    pattern = "bca";
+    if (kmp(pattern, text) == true) {
+        std::cout << "Found" << std::endl;
+    } else {
+        std::cout << "Not Found" << std::endl;
     }
+
     return 0;
 }
-