最长公共子串 (输出子串)

题目链接：https://cn.vjudge.net/contest/318888#problem/I

题意：

求两个字符串的最长公共子串并且输出

思路：

和求最长公共子串的思路是一样的，就是多一个记录位置的操作。

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <queue>
#include <set>

#define INF 0x3f3f3f3f
#define pii pair<int,int>
#define LL long long
using namespace std;
typedef unsigned long long ull;
const int MAXN = 200005;

int wa[MAXN], wb[MAXN], wv[MAXN], ws_[MAXN];
void Suffix(int *r, int *sa, int n, int m)
{
    int i, j, k, *x = wa, *y = wb, *t;
    for(i = 0; i < m; ++i) ws_[i] = 0;
    for(i = 0; i < n; ++i) ws_[x[i] = r[i]]++;
    for(i = 1; i < m; ++i) ws_[i] += ws_[i - 1];
    for(i = n - 1; i >= 0; --i) sa[--ws_[x[i]]] = i;
    for(j = 1, k = 1; k < n; j *= 2, m = k)
    {
        for(k = 0, i = n - j; i < n; ++i) y[k++] = i;
        for(i = 0; i < n; ++i) if(sa[i] >= j) y[k++] = sa[i] - j;
        for(i = 0; i < n; ++i) wv[i] = x[y[i]];
        for(i = 0; i < m; ++i) ws_[i] = 0;
        for(i = 0; i < n; ++i) ws_[wv[i]]++;
        for(i = 1; i < m; ++i) ws_[i] += ws_[i - 1];
        for(i = n - 1; i >= 0; --i) sa[--ws_[wv[i]]] = y[i];
        t = x;
        x = y;
        y = t;
        for(x[sa[0]] = 0, i = k = 1; i < n; ++i)
            x[sa[i]] = (y[sa[i - 1]] == y[sa[i]] && y[sa[i - 1] + j] == y[sa[i] + j]) ? k - 1 : k++;
    }
}
int Rank[MAXN], height[MAXN], sa[MAXN], r[MAXN];
void calheight(int *r,int *sa,int n)
{
    int i,j,k=0;
    for(i=1; i<=n; i++)Rank[sa[i]]=i;
    for(i=0; i<n; height[Rank[i++]]=k)
        for(k?k--:0,j=sa[Rank[i]-1]; r[i+k]==r[j+k]; k++);
}
int n,minnum[MAXN][17];
void RMQ()
{
    int i,j;
    int m=(int)(log(n*1.0)/log(2.0));
    for(i=1;i<=n;i++)
        minnum[i][0]=height[i];
    for(j=1;j<=m;j++)
        for(i=1;i+(1<<j)-1<=n;i++)
            minnum[i][j]=min(minnum[i][j-1],minnum[i+(1<<(j-1))][j-1]);
}
int Ask_MIN(int a,int b)
{
    int k=int(log(b-a+1.0)/log(2.0));
    return min(minnum[a][k],minnum[b-(1<<k)+1][k]);
}
int calprefix(int a,int b)
{
    a=Rank[a],b=Rank[b];
    if(a>b)
        swap(a,b);
    return Ask_MIN(a+1,b);
}
char s[MAXN];
int q[MAXN];
int main()
{
    int k;
    cin >> k;
    cin >> s;
    s[k] = '#';
    cin >> (s+k+1);
    int n = strlen(s);
    for (int i=0;i<n;i++){
        r[i] = s[i];
    }
    int maxx = 0;
    Suffix(r,sa,n+1,258);
    calheight(r,sa,n);
    int x,y;
    for (int i=1;i<=n;i++) {
        if (height[i] > maxx && 1ll * (sa[i] - k) * (sa[i - 1] - k) < 0){
            maxx = height[i];
            x = min(sa[i],sa[i-1]);
            y = x+maxx;
        }
    }
    for (int i=x;i<y;i++){
        printf("%c",s[i]);
    }
    return 0;
}