Problem Link : http://www.spoj.com/problems/LCS/
Solution Idea:
This is the problem no 6 on Suffix array paper .
The question need to find the maximum value of LCP[] array between two consecutive suffixes where this two consecutive suffixes are from different input string.
#include <bits/stdc++.h> #define pii pair <int,int> #define pll pair <long long,long long> #define sc scanf #define pf printf #define Pi 2*acos(0.0) #define ms(a,b) memset(a, b, sizeof(a)) #define pb(a) push_back(a) #define MP make_pair #define db double #define ll long long #define EPS 10E-10 #define ff first #define ss second #define sqr(x) (x)*(x) #define D(x) cout<<#x " = "<<(x)<<endl #define VI vector <int> #define DBG pf("Hi\n") #define MOD 1000000007 #define CIN ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0) #define SZ(a) (int)a.size() #define sf(a) scanf("%d",&a) #define sfl(a) scanf("%lld",&a) #define sff(a,b) scanf("%d %d",&a,&b) #define sffl(a,b) scanf("%lld %lld",&a,&b) #define sfff(a,b,c) scanf("%d %d %d",&a,&b,&c) #define sfffl(a,b,c) scanf("%lld %lld %lld",&a,&b,&c) #define stlloop(v) for(__typeof(v.begin()) it=v.begin();it!=v.end();it++) #define loop(i,n) for(int i=0;i<n;i++) #define loop1(i,n) for(int i=1;i<=n;i++) #define REP(i,a,b) for(int i=a;i<b;i++) #define RREP(i,a,b) for(int i=a;i>=b;i--) #define TEST_CASE(t) for(int z=1;z<=t;z++) #define PRINT_CASE printf("Case %d: ",z) #define LINE_PRINT_CASE printf("Case %d:\n",z) #define CASE_PRINT cout<<"Case "<<z<<": " #define all(a) a.begin(),a.end() #define intlim 2147483648 #define infinity (1<<28) #define ull unsigned long long #define gcd(a, b) __gcd(a, b) #define lcm(a, b) ((a)*((b)/gcd(a,b))) using namespace std; /*----------------------Graph Moves----------------*/ //const int fx[]={+1,-1,+0,+0}; //const int fy[]={+0,+0,+1,-1}; //const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1}; // Kings Move //const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1}; // Kings Move //const int fx[]={-2, -2, -1, -1, 1, 1, 2, 2}; // Knights Move //const int fy[]={-1, 1, -2, 2, -2, 2, -1, 1}; // Knights Move /*------------------------------------------------*/ /*-----------------------Bitmask------------------*/ //int Set(int N,int pos){return N=N | (1<<pos);} //int reset(int N,int pos){return N= N & ~(1<<pos);} //bool check(int N,int pos){return (bool)(N & (1<<pos));} /*------------------------------------------------*/ #define mx 500005 int SA[mx],tempSA[mx]; int RA[mx],tempRA[mx]; int c[mx]; int Phi[mx],PLCP[mx],LCP[mx]; char str[mx],str1[mx]; int n; void counting_sort(int k) { int maxi=max(n,300); ms(c,0); for(int i=0; i<n; i++) { int a=i+k<n?RA[i+k]:0; c[a]++; } for(int i=0,sum=0; i<maxi; i++) { int x=c[i]; c[i]=sum; sum+=x; } for(int i=0; i<n; i++) { int a=SA[i]+k<n?RA[SA[i]+k]:0; int b=c[a]; c[a]++; tempSA[b]=SA[i]; } for(int i=0; i<n; i++) SA[i]=tempSA[i]; } void build_SA() { for(int i=0; i<n; i++) { RA[i]=str[i]; SA[i]=i; } for(int k=1; k<n; k*=2) { counting_sort(k); counting_sort(0); int r=0; tempRA[SA[0]]=r=0; for(int i=1; i<n; i++) { if(RA[SA[i]]==RA[SA[i-1]] && RA[SA[i]+k]==RA[SA[i-1]+k]) tempRA[SA[i]]=r; else tempRA[SA[i]]=++r; } for(int i=0; i<n; i++) RA[i]=tempRA[i]; if(RA[SA[n-1]]==n-1) break; } } void build_LCP() { Phi[SA[0]]=-1; for(int i=1; i<n; i++) Phi[SA[i]]=SA[i-1]; for(int i=0,L=0; i<n; i++) { if(Phi[i]==-1) { PLCP[i]=0; continue; } while(str[i+L]==str[Phi[i]+L]) L++; PLCP[i]=L; L=max(L-1,0); } for(int i=0; i<n; i++) LCP[i]=PLCP[SA[i]]; } int main() { // freopen("in.txt","r",stdin); // freopen("out.txt","w",stdout); int pos; scanf("%s %s",str,str1); strcat(str,"$"); pos=strlen(str)-1; strcat(str,str1); strcat(str,"#"); n=strlen(str); build_SA(); build_LCP(); // string ss=str; // for(int i=0;i<n;i++) // cout<<SA[i]<<" "; // cout<<endl; // for(int i=0;i<n;i++) // cout<<LCP[i]<<" "; // cout<<endl; // for(int i=0;i<n;i++) // cout<<ss.substr(SA[i])<<endl; int ans=0; for(int i=1; i<n; i++) { if((SA[i]<pos && (SA[i-1]>pos)) || ((SA[i]>pos && SA[i-1]<pos))) { ans=max(ans,LCP[i]); } } pf("%d\n",ans); return 0; }