Create RabinKarp.cpp

Author: ps-19

RabinKarp.cpp

@@ -0,0 +1,70 @@
+#include <bits/stdc++.h>
+using namespace std;
+#define fastio() ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
+#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
+#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
+#define ll  long long
+#define int long long
+#define ld  long double
+#define endl "\n"
+#define pb  push_back
+#define fill(a,val) memset(a,val,sizeof(a))
+#define ff  first
+#define ss  second
+#define test  ll t; cin>>t; while(t--)
+#define loop(i,a,b)  for(ll i=a;i<b;i++)
+#define loopr(i,a,b) for(ll i=a;i>=b;i--)
+#define pii pair<ll,ll>
+#define all(v) v.begin(),v.end()
+const ll mod     = 1000*1000*1000+7;
+const ll inf     = 1ll*1000*1000*1000*1000*1000*1000 + 7;
+const ll mod2    = 998244353;
+const ll N       = 1000 * 1000 + 10;
+const ld pi      = 3.141592653589793;
+ll power(ll x,ll y,ll p = LLONG_MAX ){ll res=1;x%=p;while(y>0){if(y&1)res=(res*x)%p;y=y>>1;x=(x*x)%p;}return res;}
+ll ncr(ll n,ll r,ll m){if(r>n)return 0;ll a=1,b=1,i;for(i=0;i<r;i++){a=(a*n)%m;--n;}while(r){b=(b*r)%m;--r;}return (a*power(b,m-2,m))%m;}
+
+void pre(map<char,ll> &mp){
+    for(char i='a';i<='z';i++){
+        mp[i]=i-'a'+1;
+    }
+}
+ll rabin_karp(string s,string p){
+    map<char,ll> mp;
+    pre(mp);
+    ll n=s.length(), m=p.length();
+    ll hashcode=0,cnt=0;
+    for(ll i=0;i<m;i++){
+        hashcode=(hashcode%mod + (mp[p[i]]%mod*power(26,m-i,mod)%mod)%mod)%mod;
+        hashcode%=mod;
+    }
+    ll value=0;
+    for(ll i=0;i<m-1;i++){
+        value=value%mod+(mp[s[i]]*power(26,m-i,mod)%mod)%mod;
+        value%=mod;
+    }
+    for(ll i=m-1;i<n;i++){
+        value=(value%mod+mp[s[i]]*26)%mod;
+        value%=mod;
+        if(value==hashcode){
+            cnt++;
+            cout<<"occured here between: "<<i-m+1<<" "<<i<<endl;
+        }
+        value=(value-(mp[s[i-m+1]]*power(26,m,mod)%mod)%mod+mod)%mod;
+        value%=mod;
+        value=(value%mod*26)%mod;
+        value%=mod;
+    }
+    return cnt;
+}
+void solve(){
+    string s,p;
+    cin>>s>>p;
+    cout<<rabin_karp(s,p)<<endl;
+}
+signed main(){
+    fastio();
+    // test
+    solve();
+    return 0;
+}