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