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  1.     /*
  2.     --------------------------------DO NOT COPY I REQUEST YOU PLEASE--------------------------
  3.      
  4.     AUTHOR : Chandan Agrawal
  5.     College : Poornima College of Engg. jaipur, Raj
  6.     Mail : chandanagrawal23@gmail.com
  7.      
  8.     */
  9.  
  10.     #include<bits/stdc++.h>
  11.     #include<stdio.h>
  12.     using namespace std;
  13.  
  14.     #define fastio ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
  15.     #define MAX 100050
  16.  
  17.     #define ll long long
  18.     #define ld long double
  19.     #define lli long int
  20.  
  21.     #define pb emplace_back
  22.     #define INF 1000000000
  23.     #define mod 1000000007
  24.     #define MOD 1000000007
  25.  
  26.     // trignometric function always give value in Radians only
  27.     #define PI acos(-1) //3.1415926535897932384626433832795028
  28.     #define dsin(degree) sin(degree*(PI/180.0))
  29.     #define dcos(degree) cos(degree*(PI/180.0))
  30.     #define dtan(degree) tan(degree*(PI/180.0))
  31.  
  32.     #define rsin(radian) sin(radian)
  33.     #define rcos(radian) cos(radian)
  34.     #define rtan(radian) tan(radian)
  35.  
  36.     #define loop(i,n) for (lli i = 0; i < n; i++)
  37.     #define loopitr(xt,vec) for (auto xt : vec)
  38.     #define FOR(i,a,b) for (lli i = a; i < b; i+=1)
  39.     #define loop_rev(i,n) for (lli i = n-1; i >= 0; i--)
  40.     #define FOR_REV(i,a,b) for (lli i = a; i >= b; i--)
  41.     #define itr :: iterator it
  42.     #define WL(t) while(t --)
  43.  
  44.     #define all(v) v.begin(),v.end()
  45.     #define makeuniq(v) v.resize(unique(all(v)) - v.begin()); //only uniq element in vector after this
  46.     #define sz(x) int(x.size())
  47.     #define F first
  48.     #define S second
  49.  
  50.     #define mii map<lli,lli>
  51.     #define vi vector<lli>
  52.     #define seti set<lli>
  53.     #define pii pair<lli,lli>
  54.  
  55.     #define gcd(a,b) __gcd((a),(b))
  56.     #define lcm(a,b) (a/gcd(a,b))*b
  57.     #define abs(x) ((x < 0)?-(x):x)
  58.  
  59.     template <typename T>
  60.     void print(T x){cout<<x<<endl;}
  61.     template <typename T1, typename T2>
  62.     void print2(T1 x,T2 y){cout<<x<<" "<<y<<endl;}
  63.     template <typename T1, typename T2,typename T3>
  64.     void print3(T1 x, T2 y,T3 z){cout<<x<<" "<<y<<" "<<z<<endl;}
  65.  
  66.     #define scanarr(a,n) for(lli i=0;i<n;i++)    cin>>a[i];
  67.     #define scanvector(a,n) for(lli i=0;i<n;i++){ lli x ; cin>>x; a.push_back(x);}
  68.  
  69.     #define printarr(a,n) for(lli i=0;i<n;i++)   cout<<a[i]<<" "; cout<<endl;
  70.     #define printvector(vec) for(auto xt : vec) cout<<xt<<" ";    cout<<"\n";
  71.     #define printset(st) for(auto xt : st) cout<<xt<<" ";    cout<<"\n";
  72.  
  73.     #define FD(N) fixed<<setprecision(N)
  74.  
  75.     #define endl '\n'
  76.  
  77.     #define deb(x) cout<<#x<<" "<<x<<endl;
  78.  
  79.     /*
  80.     ifstream cinn("i3.txt");
  81.     ofstream coutt("o3.txt");
  82.     */
  83.  
  84.  
  85.     bool isvowel(char v) { return (0x208222>>(v&0x1f))&1; }
  86.  
  87.     lli mceil(lli a,lli b){
  88.         if(a%b==0) return(a/b);
  89.         else return(a/b  +1);
  90.     }
  91.     lli mfloor(lli a,lli b){
  92.         return(a/b);
  93.     }
  94.  
  95.     ll modmul(ll a, ll b) {
  96.         return ((a%mod) * (b%mod)) % mod;
  97.     }
  98.  
  99.     ll modadd(ll a , ll b){
  100.         return((a%mod)+(b%mod)+mod)%mod;
  101.     }
  102.  
  103.     ll modsub(ll a , ll b){
  104.         return((a%mod) - (b%mod) + mod)%mod;
  105.     }
  106.  
  107.     lli fastexpo(lli a,lli b){
  108.         a = a%mod;
  109.         lli ans=1;
  110.         while(b){
  111.             if(b&1)
  112.                 ans=(ans*1ll*a)%mod;
  113.             a=(a*1ll*a)%mod;
  114.             b=b/2;
  115.             }
  116.         return ans;
  117.      }
  118.  
  119.  
  120.  
  121.      /* -----------------------------------------------------HASHING-------------------------------------------------------------------*/
  122.     /*
  123.     some key points -
  124.     1. Use (long int) to remove TLE or Memory Limit issue
  125.     2. If still Wrong answer then may be collision occur , use p as bigger prime no. p : [31,53,107,209,4793]
  126.     3. use mod either 1e9+7
  127.     4 .If it still shows WA then surely collision occurs use Double Hashing
  128.        Double Hashing -
  129.             Make Prehash Array using two different p and mod so chances of collision is less
  130.     5. use pass by reference always
  131.      
  132.      
  133.     */
  134.  
  135.     #define maxlen 1000005 //maximum length of string
  136.  
  137.     lli pow_p[maxlen]; // p^i %m
  138.     lli p_inv[maxlen]; // this is inverse_Mod(p^i) basically p^(-n) =  [p^(-1) ]^n so calculate just p^(-1) and caluclate power
  139.                    // like inversemod(p^(-2)) = p^(-1) * p^(-1)
  140.     void init(lli p)
  141.     {
  142.         pow_p[0]=1;
  143.         p_inv[0]=1;
  144.         lli pinv = fastexpo(p,mod-2);
  145.         for(lli i=1;i<maxlen;i++)
  146.         {
  147.             pow_p[i] = modmul(pow_p[i-1],p);
  148.             p_inv[i] = modmul(p_inv[i-1],pinv);
  149.         }
  150.  
  151.     }
  152.  
  153.     struct Hash{
  154.             // 0 based indexing
  155.             lli prehash[maxlen];
  156.             // hash(s) = sigma(i=0 to n-1) s[i]*p^(i)
  157.             // a->1 , b->2 , c->3 and so on
  158.  
  159.  
  160.             void precomputehash(string &s){ //p can be any prime 19 , 31, 53,107 ...
  161.  
  162.  
  163.                 prehash[0]=(s[0])+1;
  164.                 for (lli i=1;i<s.size();i++) {
  165.                     prehash[i]= modadd(prehash[i-1] , modmul((s[i]+1),pow_p[i]));
  166.                 }
  167.             }
  168.  
  169.             // hash[l..r] = ((hash[upto r] - hash[upto (l-1)] ) / P^l) % mod = ((hash[upto r] - hash[upto (l-1)] ) * modinv(P^l) )%mod
  170.             lli gethash(lli l, lli r){
  171.                 if(l==0)
  172.                     return(prehash[r]%mod);
  173.                 else{
  174.                     lli ans = modsub(prehash[r],prehash[l-1]);
  175.                     ans = modmul(ans, p_inv[l]);
  176.                     return ans;
  177.                 }
  178.             }
  179.  
  180.             // hash value of all string means hash[0..(n-1)] // 0 based indexing
  181.             lli totalhash(string &s){
  182.                 return(prehash[sz(s)-1]%mod);
  183.             }
  184.     }; 
  185.  
  186.  
  187.  
  188.     bool check(string &a , string &b , Hash &obja , Hash &objb , lli len)
  189.     {
  190.         unordered_set<lli> st;
  191.         for(lli i=0;i<=sz(a)-len;i++)
  192.             st.insert(obja.gethash(i,i+len-1));
  193.  
  194.         for(lli i=0;i<=sz(b)-len;i++)
  195.         {
  196.             if(st.find(objb.gethash(i,i+len-1)) != st.end())
  197.                 return true;
  198.         }
  199.         return false;
  200.  
  201.     }
  202.  
  203.  
  204.     int main(){
  205.     fastio
  206.     lli t=1;
  207.     //cin>>t;
  208.     init(53);
  209.     while(t--) {
  210.         string aa,bb,a,b;
  211.         cin>>aa>>bb;
  212.         if(sz(aa)>sz(bb))
  213.         {
  214.             a=aa;
  215.             b=bb;
  216.         }
  217.         else
  218.         {
  219.             a=bb;
  220.             b=aa;
  221.         }
  222.         Hash obja , objb;
  223.         obja.precomputehash(a);
  224.         objb.precomputehash(b);
  225.  
  226.         lli ans = 0;
  227.         lli l = 0;
  228.         lli r = sz(b);
  229.         while(l<=r)
  230.         {
  231.             lli mid = (l+r)/2;
  232.             if(check(a,b,obja,objb,mid))
  233.             {
  234.                 l = mid+1;
  235.                 ans = mid;
  236.             }
  237.             else
  238.             {
  239.                 r = mid-1;
  240.             }
  241.         }
  242.         print(ans);
  243.  
  244.       }
  245.     return 0;
  246.     }
Success #stdin #stdout 0.01s 19064KB
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https://ideone.com/HJNFI7
language:
C++14 (gcc 8.3)
created:
5 years ago
visibility:
public

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