Merge pull request #277 from mahbubcseju/master

Added knuth pratt morris algorithm for finding string match.

String/knuth_morris_pratt.cpp

+/*
+    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
+*/
+
+#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];
+        }
+        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];
+        }
+        k++;
+        if(k==pattern_length)return true;
+    }
+    return false;
+}
+
+int main()
+{   
+   
+    string text="alskfjaldsabc1abc1abc12k23adsfabcabc";
+    string pattern="abc1abc12l";
+    if(kmp(pattern,text)==true){
+        cout<<"Found"<<endl;
+    }
+    else{
+        cout<<"Not Found"<<endl;
+    }
+    text="abcabc";
+    pattern="bca";
+    if(kmp(pattern,text)==true){
+        cout<<"Found"<<endl;
+    }
+    else{
+        cout<<"Not Found"<<endl;
+    }
+    return 0;
+}
+