字符串

目录

• KMP
• 字典树，trie树
• 马拉车
• AC自动机

KMP

#include <cstdio>
#include <cstring>
#define R register
const int MAXN=1000007;
int l,l1;
char s[MAXN],s1[MAXN];
int fail[MAXN];
inline void get_next()
{
	int p=0;
	for(R int i=2;i<=l;++i)
	{
		while(p>0&&s[i]!=s[p+1]) p=fail[p];
		if(s[i]==s[p+1]) p++;
		fail[i]=p;
	}
}

inline void kmp()
{
	int p=0;
	for(R int i=1;i<=l1;++i)
	{
		while(p>0&&s[p+1]!=s1[i]) p=fail[p];
		if(s[p+1]==s1[i]) p++;
		if(p==l)
		{
			printf("%d\n",i-l+1);
			p=fail[p];
		}
	}
}

int main()
{
	scanf("%s%s",s1+1,s+1);
	l=strlen(s+1);
	l1=strlen(s1+1);
	get_next();
	kmp();
	for(int i=1;i<=l;++i)
		printf("%d ",fail[i]);
	return 0;
}

字典树，trie树

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

int n;
struct node {
	int next[27];
	bool w;
} a[300000];
int tot;
bool flag[300000];

void build(char *b) {
	int p=0,len=strlen(b);
	for(int i=0; i<len; ++i) {
		int x=b[i]-'a';
		if(!a[p].next[x]) {
			a[p].next[x]=++tot;
		}
		p=a[p].next[x];
	}
	flag[p]=1;
}

void find(char *b) {
	int p=0,len=strlen(b);
	for(int i=0; i<len; ++i) {
		int x=b[i]-'a';
		if(!a[p].next[x]) {
			printf("NO\n");
			return;
		}
		p=a[p].next[x];
	}
	if(flag[p]) printf("YES\n");
	else printf("NO\n");
}

int main() {
	int n,m;
	char s[100];
	scanf("%d",&n);
	for(int i=1; i<=n; ++i)
		scanf("%s",s),build(s);
	scanf("%d",&m);
	while(m--)
		scanf("%s",s),find(s);
	return 0;
}

马拉车

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int maxn=11000007;
char s[maxn],S[maxn];
int p[maxn<<1];
int main()
{
	scanf("%s",s);
	S[0]='@';S[1]='#';
	int l=1,i=-1;
	while(s[++i]!='\0')
		S[++l]=s[i],S[++l]='#';
	int mx=0,id=0,ans=0;
	for(int i=1;i<=l;++i)
	{
		if(mx>i) p[i]=min(p[id*2-i],mx-i);//id*2-i即i-k
		else p[i]=1;
		while(S[i+p[i]]==S[i-p[i]]) p[i]++;
		if(mx<i+p[i]-1) mx=i+p[i]-1,id=i;
		ans=max(p[i]-1,ans);
	}
	printf("%d",ans);
	return 0;
}

AC自动机

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<cmath>
#include<queue>
using namespace std;
const int N=2000100;
struct Tree{
    int fail,end; 
    int vis[27]; 
}e[N]; 

int cnt,n;
char s[N];

inline int read() {
    int n=0,f=1;char ch=getchar();
    while (ch<'0'||ch>'9') {if(ch=='-') f=-1;ch=getchar();}
    while (ch<='9'&&ch>='0') {n=n*10+ch-'0';ch=getchar();}
    return n*f;
}

inline void insert(char *s) {
    int n=strlen(s);
    int now=0;
    for(int i=0;i<n;++i) {
        int tmp=s[i]-'a';
        if(!e[now].vis[tmp]) e[now].vis[tmp]=++cnt;
        now=e[now].vis[tmp];
    }
    e[now].end++;
} 

inline void build() {
    queue<int> q;
    for(int i=0;i<26;++i)
        if(e[0].vis[i])
            q.push(e[0].vis[i]),e[e[0].vis[i]].fail=0;
    while(!q.empty()) {
        int u=q.front();
        q.pop();
        for(int i=0;i<26;++i)
            if(e[u].vis[i]) {
                e[e[u].vis[i]].fail=e[e[u].fail].vis[i];
                q.push(e[u].vis[i]);	
            }
            else e[u].vis[i]=e[e[u].fail].vis[i];
    }
}

inline void query(char *s) {
    int l=strlen(s);
    int now=0,ans=0; 
    for(int i=0;i<l;++i) {
        int now=e[now].vis[s[i]-'a'];
        for(int t=now;t&&e[t].end!=-1;t=e[t].fail) {
            ans+=e[t].end;
            e[t].end=-1; 
        } 
    }
    printf("%d\n",ans); 
} 

int main() {
    n=read();
    for(int i=1;i<=n;++i) cin>>s,insert(s);
    build();
    cin>>s;
    query(s); 
    return 0; 
}