ural 1517. Freedom of Choice (后缀数组，最长公共子串)

ural1517
题意：给出两个字符串，求最长的公共字串（要求出具体的字符串是什么）

思路：依然是后缀数组，在更新长度 的时候记录起始位置即可，1A。以及，发现多开了一个完全没有必要的数组w[],这次已删。

 

20160730update:模板已更正，lrj的模板的rk[i]为0 的时候会出现re的问题…已特判。

C++
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/* ***********************************************
Author :111qqz
Created Time :2016年07月31日 星期日 00时36分19秒
File Name :code/ural/1517.cpp
************************************************ */
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <cmath>
#include <cstdlib>
#include <ctime>
#define fst first
#define sec second
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define ms(a,x) memset(a,x,sizeof(a))
typedef long long LL;
#define pi pair < int ,int >
#define MP make_pair
using namespace std;
const double eps = 1E-8;
const int dx4[4]={1,0,0,-1};
const int dy4[4]={0,-1,1,0};
const int inf = 0x3f3f3f3f;
const int N=2E5+7;
char s[N];
int n,sa[N],rk[N],t[N],t2[N],cnt[N];
int height[N];
int cmp(int *r,int a,int b,int l)  {return r[a]==r[b]&&r[a+l]==r[b+l];}
void getSa(int n,int m)
{
    int *x = t,*y= t2;
    ms(cnt,0);
    for ( int i = 0 ; i < n ; i++) cnt[x[i]=s[i]]++;
    for ( int i = 1 ; i < m ; i++) cnt[i]+=cnt[i-1];
    for ( int i = n-1 ; i >= 0 ; i--) sa[--cnt[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;
        ms(cnt,0);
        for ( int i = 0 ; i < n;  i++) cnt[x[y[i]]]++;
        for ( int i = 0 ; i < m ; i++) cnt[i]+=cnt[i-1];
        for ( int i = n-1 ; i >= 0 ; i--) sa[--cnt[x[y[i]]]] = y[i];
        swap(x,y);
        p = 1;
        x[sa[0]] = 0;
        for ( int i = 1 ; i < n ; i++)
            x[sa[i]] = cmp(y,sa[i-1],sa[i],k)?p-1:p++;
        if (p>=n) break;
        m = p;
    }
}
void getHeight( int n)
{
    int k = 0 ;
    for ( int i = 0 ; i < n ; i++) rk[sa[i]] = i ;
    height[0] = 0 ;
    for ( int i = 0 ; i < n ; i++)
    {
        if (rk[i]==0) continue;
        if (k) k--;
        int j = sa[rk[i]-1];
        while (s[i+k]==s[j+k]) k++;
        height[rk[i]] = k ;
    }
}
int getSuffix(char s[])
{
    int len = strlen(s);
    int up = 0 ;
    for ( int i = 0 ; i < len ; i++)
    {
        int val = s[i];
        up = max(up,val);
    }
    getSa(len,up+1);
    getHeight(len);
    return len;
}
int main()
{
        #ifndef  ONLINE_JUDGE
        freopen("code/in.txt","r",stdin);
  #endif
        string st1,st2,st;
        int len1,len;
        cin>>len1>>st1>>st2;
        st = st1+"$"+st2;
        strcpy(s,st.c_str());
        len = getSuffix(s);
        int ans = 0 ,beg=0;
        for ( int i = 2 ; i < len ; i++)
            if (height[i]>ans)
            {
                if (0<=sa[i-1]&&sa[i-1]<len1&&len1<sa[i])
                {
                    beg = sa[i-1];
                    ans = height[i];
                }
                if (0<=sa[i]&&sa[i]<len1&&len1<sa[i-1])
                {
                    beg = sa[i];
                    ans = height[i];
                }
            }
        cout<<st1.substr(beg,ans)<<endl<<endl;
  #ifndef ONLINE_JUDGE  
  fclose(stdin);
  #endif
    return 0;
}
 
 
 
 

作者： CrazyKK

ex-ACMer@hust，stackoverflow-engineer@sensetime

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