Added KMP algorithm

C++/KMP Algorithm.cpp

@@ -0,0 +1,60 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+/*build longest prefix-suffix array for seq to be searched*/
+vector<int> LPS(string s)
+{
+    int n=s.size();
+    vector<int> pi(n);
+    pi[0]=0;
+    for(int i=1;i<n;i++)
+    {
+        int j = pi[i-1];
+        while (j > 0 && s[i] != s[j])
+        j = pi[j-1];
+        if (s[i] == s[j])
+        j++;
+        pi[i] = j;
+    }
+    return pi;
+}
+
+/*find all starting index where sub is found*/
+vector<int> search(string str, string sub)
+{
+    vector<int> lps=LPS(sub);
+    int i(0),j(0);
+    vector<int> ind;
+
+    while(i<str.size())
+    {
+        if(str[i]==sub[j])
+        {
+            i++;
+            j++;
+        }
+        else
+        {
+            if(j>0)
+                j=lps[j-1];
+            else
+                i++;
+        }
+        if(j==sub.size())
+        {
+            ind.push_back(i-sub.size());
+            j=lps[j-1];
+        }
+    }
+    return ind;
+}
+int main()
+{
+    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
+
+    vector<int> ans=search("anant","ant");
+    for(auto it:ans)
+        cout<<it<<" ";
+    return 0;
+}
+