Added Rabin_Karp and KMP Algorithm

Author: dhanashreeg368

Strings/KMP_Algorithm.cpp

@@ -0,0 +1,73 @@
+//KMP Algorithm - Pattern Searching Algorithm
+
+#include <iostream>
+using namespace std;
+
+// Function to implement the KMP algorithm
+void KMP(string t, string p)
+{
+    int tlen = t.length();
+    int plen = p.length();
+
+    // if `text` is an empty string
+    if (plen == 0)
+    {
+        cout << "The pattern at index 0";
+        return;
+    }
+
+    // if X's length is less than that of Y's
+    if (tlen < plen)
+    {
+        cout << "Pattern not found";
+        return;
+    }
+
+    // `next[i]` stores the index of the next best partial match
+    int next[plen + 1];
+
+    for (int i = 0; i < plen + 1; i++) {
+        next[i] = 0;
+    }
+
+    for (int i = 1; i < plen; i++)
+    {
+        int j = next[i + 1];
+
+        while (j > 0 && p[j] != p[i]) {
+            j = next[j];
+        }
+
+        if (j > 0 || p[j] == p[i]) {
+            next[i + 1] = j + 1;
+        }
+    }
+
+    for (int i = 0, j = 0; i < tlen; i++)
+    {
+        if (t[i] == p[j])
+        {
+            if (++j == plen) {
+                cout << "The pattern occurs at index " << i - j + 1 << endl;
+            }
+        }
+        else if (j > 0)
+        {
+            j = next[j];
+            i--;    // since `i` will be incremented in the next iteration
+        }
+    }
+}
+
+// Program to implement the KMP algorithm in C++
+int main()
+{
+    string text;
+    cout<<"Enter text: ";
+    cin>>text;
+    string pattern;
+    cout<<"Enter pattern: ";
+    cin>>pattern;
+    KMP(text, pattern);
+    return 0;
+}

Strings/Rabin_Karp_Algorithm.cpp

@@ -0,0 +1,70 @@
+#include <bits/stdc++.h>
+using namespace std;
+const int t = 256;
+const int w = 1283;
+void Rabin_Karp_Algo(string text,string pattern)
+{
+
+    //Length of text string.
+    int tlen = text.length();
+
+    //Length of pattern string.
+    int plen = pattern.length();
+
+    int flag;
+    int c=1,i=0;
+
+    //Calculate hash_p(hash value of pattern) and hash_0
+    int hash_p=0,hash=0;
+    for(int i=0;i<plen;i++)
+    {
+        hash_p=(hash_p*t + pattern[i])%w;
+        hash=(hash*t + text[i])%w;
+
+    }
+
+     //Calculate (t^(plen-1))%w
+    for(int i=1;i<=plen-1;i++)
+        c=(c*t)%w;
+
+    i=0;
+    while(i<=tlen-plen){
+       if(hash_p==hash){
+            flag=1;
+            for(int j=0;j<plen;j++){
+                if(pattern[j]==text[i+j]){
+                    continue;
+                }
+                else{
+                    flag = 0;
+                    break;
+                }
+           }
+            if(flag==1)
+            cout<<"Index of occurrence is "<<i<<" ";
+       }
+
+
+       //Calculate hash value of next window
+       //hash_i+1 = t * {hash_i - text[i] * t^(plen-1)} + text[i+plen]
+       if(i<tlen-plen){
+           hash=((t*(hash-text[i]*c))+text[i+plen])%w;
+            if(hash<0){
+                hash = hash + w;
+            }
+       }
+       i++;
+    }
+}
+
+int main()
+{
+    string text;
+    cout<<"Enter the text: ";
+    cin>>text;
+    string pattern;
+    cout<<"Enter the pattern: ";
+    cin>>pattern;
+    Rabin_Karp_Algo(text,pattern);
+    return 0;
+}