ural1517

题解：

后缀数组

求一下最长公共字串

代码：

#include<cstdio>
#include<cmath>
#include<algorithm>
#include<cstring> 
using namespace std;  
const int N=2000200;  
char s1[N],m,n,s2[N],ss[N]; 
int height[N],str[N],sa[N],Log[N],best[23][N],rank[N],c[N],t1[N],t2[N];  
void da(int *str,int n,int m)  
{  
    int *x=t1,*y=t2;  
    for (int i=0;i<m;i++)c[i]=0;  
    for (int i=0;i<n;i++)c[x[i]=str[i]]++;  
    for (int i=1;i<m;i++)c[i]+=c[i-1];  
    for (int i=n-1;i>=0;i--)sa[--c[x[i]]]=i;  
    for (int k=1;k<=n;k<<=1)  
     {  
        int p=0;  
        for (int i=n-k;i<n;i++)y[p++]=i;  
        for (int i=0;i<n;i++)
         if (sa[i]>=k)y[p++]=sa[i]-k;  
        for (int i=0;i<m;i++)c[i]=0;  
        for (int i=0;i<n;i++)c[x[y[i]]]++;  
        for (int i=1;i<m;i++)c[i]+=c[i-1];  
        for (int i=n-1;i>=0;i--)sa[--c[x[y[i]]]]=y[i];  
        swap(x,y);  
        p=1;x[sa[0]]=0;  
        for (int i=1;i<n;i++)  
         x[sa[i]]=y[sa[i]]==y[sa[i-1]]&&y[sa[i]+k]==y[sa[i-1]+k]?p-1:p++;  
        if (p>=n)break;  
        m=p;  
     }  
}  
void calheight(int *str,int n)  
{  
    int j,k=0;  
    for (int i=0;i<=n;i++)rank[sa[i]]=i;  
    for (int i=0;i<n;i++)  
     {  
        if (k)k--;  
        j=sa[rank[i]-1];  
        while (str[i+k]==str[j+k])k++;  
        height[rank[i]]=k;  
     }  
}  
void init(int n)  
{   
    Log[0]=-1;  
    for (int i=1;i<=n;i++)Log[i]=(i&(i-1))?Log[i-1]:Log[i-1]+1;  
    for (int i=1;i<=n;i++)best[0][i]=height[i];  
    for (int i=1;i<=Log[n];i++)  
     for (int j=1;j<=n;j++)best[i][j]=min(best[i-1][j],best[i-1][j+(1<<(i-1))]);  
}  
int lcp(int a,int b)  
{  
    a=rank[a];  
    b=rank[b];  
    if (a>b)swap(a,b);  
    a++;  
    int t=Log[b-a+1];  
    return min(best[t][a],best[t][b-(1<<t)+1]);  
}  
int main()  
{   
    while (~scanf("%d",&m))  
     {  
        scanf("%s%s",s1,s2);  
        int l1=strlen(s1);  
        int l2=strlen(s2);  
        int len=0;  
        for (int i=0;i<l1;i++)str[len++]=s1[i];  
        str[len++]=1;  
        for (int i=0;i<l2;i++)str[len++]=s2[i];  
        str[len]=0;  
        da(str,len+1,300);  
        calheight(str,len);  
        int be,ans=0;  
        for (int i=1;i<=len;i++)  
         {  
            if ((sa[i]<l1&&sa[i-1]>l1)||(sa[i]>l1&&sa[i-1]<l1))  
            if (ans<height[i])ans=height[i],be=sa[i];  
         }  
        for (int i=be;i<be+ans;i++)putchar(str[i]);  
        puts("");  
     }  
    return 0;  
}