SP1811 LCS - Longest Common Substring

\(\color{#0066ff}{ 题目描述 }\)

输入2 个长度不大于250000的字符串，输出这2 个字符串的最长公共子串。如果没有公共子串则输出0 。

\(\color{#0066ff}{输入格式}\)

两个字符串

\(\color{#0066ff}{输出格式}\)

一个整数，为 所求答案

\(\color{#0066ff}{输入样例}\)

alsdfkjfjkdsal
fdjskalajfkdsla

\(\color{#0066ff}{输出样例}\)

3

\(\color{#0066ff}{数据范围与提示}\)

none

\(\color{#0066ff}{ 题解 }\)

对第一个串建立后缀自动机

用第二个串在自动机上跑匹配

匹配一下就取max

#include<bits/stdc++.h>
using namespace std;
#define LL long long
LL in() {
    char ch; int x = 0, f = 1;
    while(!isdigit(ch = getchar()))(ch == '-') && (f = -f);
    for(x = ch ^ 48; isdigit(ch = getchar()); x = (x << 1) + (x << 3) + (ch ^ 48));
    return x * f;
}
const int maxn = 6e5 + 5;
struct SAM {
protected:
    struct node {
        node *ch[26], *fa;
        int len, siz;
        node(int len = 0, int siz = 0): fa(NULL), len(len), siz(siz) {
            memset(ch, 0, sizeof ch);
        }
    };
    node *root, *tail, *lst;
    node pool[maxn];
    void extend(int c) {
        node *o = new(tail++) node(lst->len + 1, 1), *v = lst;
        for(; v && !v->ch[c]; v = v->fa) v->ch[c] = o;
        if(!v) o->fa = root;
        else if(v->len + 1 == v->ch[c]->len) o->fa = v->ch[c];
        else {
            node *n = new(tail++) node(v->len + 1), *d = v->ch[c];
            std::copy(d->ch, d->ch + 26, n->ch);
            n->fa = d->fa, d->fa = o->fa = n;
            for(; v && v->ch[c] == d; v = v->fa) v->ch[c] = n;
        }
        lst = o;
    }
    void clr() {
        tail = pool;
        root = lst = new(tail++) node();
    }
public:
    SAM() { clr(); }
    void ins(char *s) { for(char *p = s; *p; p++) extend(*p - 'a'); }
    int match(char *s) {
        int ans = 0;
        node *o = root;
        int len = 0;
        for(char *p = s; *p; p++) {
            int pos = *p - 'a';
            if(o->ch[pos]) o = o->ch[pos], len++;
            else {
                while(o && !o->ch[pos]) o = o->fa;
                if(!o) o = root, len = 0;
                else len = o->len + 1, o = o->ch[pos];
            }
            ans = std::max(ans, len);
        }
        return ans;
    }
}sam;
char s[maxn];
int main() {
    scanf("%s", s);
    sam.ins(s);
    scanf("%s", s);
    printf("%d\n", sam.match(s));
    return 0;
}