自己写的KMP板子

//获取匹配个数
#include <bits/stdc++.h>  
using namespace std;  
const int maxn = 5005;  
int nt[maxn];  
char a[maxn], b[maxn];  
void GetNext(char b[], int blen)  
{  
    int j = 0, k = -1;  
    nt[0] = -1; --blen;  
    while(j < blen)  
    {  
        if(k == -1 || b[j] == b[k])  
        {  
            ++j; ++k;  
            nt[j] = k;
        }  
        else k = nt[k];  
    }  
}  
int KMP(char a[], char b[], int alen, int blen)  
{  
	if(alen < blen) return 0;
    int ans = 0;  
    if(blen == 1)  
    {  
        for(int i = 0; i < alen; ++i)  
        {  
            if(a[i] == b[0]) ++ans;  
        }  
        return ans;  
    }  
    int i = 0, j = 0;  
    GetNext(b, blen);  
    while(i < alen)  
    {  
        if(j == -1 || a[i] == b[j])  
        {  
            ++i; ++j;  
        }  
        else j = nt[j];  
        if(j == blen)  
        {  
            ++ans;  
            --i;  
            j = nt[j-1];  
        }  
    }  
    return ans;  
}  
int main()  
{  
    int alen, blen;  
    cin >> a >> b;  
    alen = strlen(a);  
    blen = strlen(b);  
    cout << KMP(a, b, alen, blen) << endl;  
    return 0;  
}

//判断是否存在匹配
#include <bits/stdc++.h>  
using namespace std;  
const int maxn = 5005;  
int nt[maxn];  
char a[maxn], b[maxn];  
void GetNext(char b[], int blen)  
{  
    int j = 0, k = -1;  
    nt[0] = -1; --blen;  
    while(j < blen)  
    {  
        if(k == -1 || b[j] == b[k])  
        {  
            ++j; ++k;  
            if(b[j] == b[k]) nt[j] = nt[k]; 
            else nt[j] = k;
        }  
        else k = nt[k];  
    }  
}  
int KMP(char a[], char b[], int alen, int blen)  
{
	if(alen < blen) return 0;
    if(blen == 1)  
    {  
        for(int i = 0; i < alen; ++i)  
        {  
            if(a[i] == b[0]) return 1;  
        }  
        return 0;  
    }  
    int i = 0, j = 0;  
    GetNext(b, blen);  
    while(i < alen && j < blen) 
    {  
        if(j == -1 || a[i] == b[j])  
        {  
            ++i; ++j;  
        }  
        else j = nt[j];
    }  
    if(j == blen) return 1;
    return 0;
}  
int main()  
{  
    int alen, blen;  
    cin >> a >> b;  
    alen = strlen(a);  
    blen = strlen(b);  
    if(KMP(a, b, alen, blen)) cout << "YES" << endl;
    else cout << "NO" << endl;  
    return 0;  
}

//寻找首次出现位置
#include <bits/stdc++.h>  
using namespace std;  
const int maxn = 5005;  
int nt[maxn];  
char a[maxn], b[maxn];  
void GetNext(char b[], int blen)  
{  
    int j = 0, k = -1;  
    nt[0] = -1; --blen;  
    while(j < blen)  
    {  
        if(k == -1 || b[j] == b[k])  
        {  
            ++j; ++k;  
            if(b[j] == b[k]) nt[j] = nt[k]; 
            else nt[j] = k;
        }  
        else k = nt[k];  
    }  
}  
int KMP(char a[], char b[], int alen, int blen)  
{
	if(alen < blen) return -1;
    if(blen == 1)  
    {  
        for(int i = 0; i < alen; ++i)  
        {  
            if(a[i] == b[0]) return i;  
        }  
        return -1;  
    }  
    int i = 0, j = 0;  
    GetNext(b, blen);  
    while(i < alen && j < blen) 
    {  
        if(j == -1 || a[i] == b[j])  
        {  
            ++i; ++j;  
        }  
        else j = nt[j];
    }  
    if(j == blen) return i-blen;
    return -1;
}  
int main()  
{  
    int alen, blen;  
    cin >> a >> b;  
    alen = strlen(a);  
    blen = strlen(b);  
    cout << KMP(a, b, alen, blen) << endl;
    return 0;  
}

//寻找所有匹配成功的在主串中的起点
#include <bits/stdc++.h>  
using namespace std;  
const int maxn = 5005;  
int nt[maxn];  
char a[maxn], b[maxn];  
vector<int> vt;
void GetNext(char b[], int blen)  
{  
    int j = 0, k = -1;  
    nt[0] = -1; --blen;  
    while(j < blen)  
    {  
        if(k == -1 || b[j] == b[k])  
        {  
            ++j; ++k;  
            nt[j] = k;
        }  
        else k = nt[k];  
    }  
}  
void KMP(char a[], char b[], int alen, int blen)  
{  
    if(alen < blen) return; 
    if(blen == 1)  
    {  
        for(int i = 0; i < alen; ++i)  
        {  
            if(a[i] == b[0]) vt.push_back(i);  
        }  
        return;  
    }  
    int i = 0, j = 0;  
    GetNext(b, blen);  
    while(i < alen)  
    {  
        if(j == -1 || a[i] == b[j])  
        {  
            ++i; ++j;  
        }  
        else j = nt[j];  
        if(j == blen)  
        {  
            vt.push_back(i-blen); 
            --i;  
            j = nt[j-1];  
        }  
    }
}  
int main()  
{  
    int alen, blen;  
    cin >> a >> b;  
    alen = strlen(a);  
    blen = strlen(b);  
    KMP(a, b, alen, blen);
    for(int i = 0; i < vt.size(); ++i) cout << vt[i] << " ";
    cout << endl; 
    return 0;  
}

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