Create Rolling_Hash_Function.cpp

Rolling_Hash_Function.cpp

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+/* https://www.codechef.com/COOK118B/problems/CHEFSHIP 
+*/
+
+
+#include<bits/stdc++.h>
+using namespace std;
+
+#define ll long long
+
+ll p =31;
+ll h[100001];
+ll power[100001];
+
+ll mod = 1e9+7;
+
+// we will store hash value of strings till ith length in h[] array
+
+void generate_hash(string s)
+{
+    h[0] = s[0]-'a'+1;
+    power[0]=1;
+    for(int i=1;i<s.length();i++)
+    {
+        power[i] = ((power[i-1]%mod)*(p%mod))%mod;
+        h[i] = ( h[i-1]%mod + ((s[i]-'a'+1)%mod *(power[i]%mod))%mod)%mod;
+    }
+}
+
+ll getHash(int l,int r)
+{
+    if(l==0)
+        return h[r]%mod;
+    else
+        return (h[r]-h[l-1]+mod)%mod;
+}
+
+int main()
+{
+    int t;
+    cin>>t;
+    while(t--)
+    {
+        string s;
+        cin>>s;
+        int n=s.length();
+        int cnt =0;
+        generate_hash(s);
+        for(int i=1;i<n-1;i+=2)
+        {
+            int id1 = i/2;
+            int id2 = (i+n)/2;
+
+            bool t1 = (getHash(0,id1)*power[id1+1])%mod == getHash(id1 + 1, i);
+            bool t2 = (getHash(i+1,id2)*power[id2-i])%mod == getHash(id2+1, n-1);
+
+            if(t1 && t2)
+                cnt++;
+        }
+        cout<<cnt<<endl;
+    }
+    return 0;
+}