kmp学习笔记

kmp学习笔记

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说再前边

字符串水平基本为0，学了第4遍KMP了，总是忘。。。网上资料很多，就不详细讲解了。

一些知识

1. 循环节大小：n - nxt[n]

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模板[HDU2087]

下标从0开始
nxt[i] 为满足p[i-z...i-1]=p[0...z-1]最大的z值

#include <cstdio>
#include <cstring>
#define rep(i,a,b) for(int i=a;i<=b;++i)
typedef long long ll;
const int N = 100000 + 7;
using namespace std;
char s[N], p[N];
int nxt[N], n, m;
void getnxt() {
    int i, j;
    j = nxt[0] =-1;
    i = 0;
    while(i < m) {
        while(j != -1 && p[i] != p[j]) j = nxt[j];
        nxt[++i] = ++j;
    }
}
int kmp_ct() {
    int i, j;
    int ans = 0;
    i = j = 0;
    while(i <= n) {
        while(j != -1 && s[i] != p[j]) j = nxt[j];
        ++i; ++j;
        if(j >= m) {
            ++ans;
            j = 0;//不可重叠
            //j = nxt[j] 可以重叠
        }
    }
    return ans;
}
int main() {
    while(~scanf(" %s", s)) {
        if(s[0] == '#') break;
        scanf(" %s", p);
        n = strlen(s), m = strlen(p);
        getnxt();
        printf("%d\n",kmp_ct());
    }
    return 0;
}

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下标从1开始

#include <cstdio>
#include <cstring>
using namespace std;
const int N=1e6+5;
int T,nxt[N],n,m;
char s[N],p[N];
void getnxt(char p[],int n){
    nxt[1]=0;
    for(int i=2;i<=n;i++){
        int j=nxt[i-1];
        while(j&&s[j+1]!=s[i]) j=nxt[j];
        if(s[j+1]==s[i]) nxt[i]=j+1;
        else nxt[i] = 0;
    }
}
int kmp(){
    int ans=0;
    getnxt(p,m);
    int j=0;
    for(int i=1;i<=n;i++){
        while(j&&p[j+1]!=s[i]) j=nxt[j];
        if(p[j+1]==s[i])++j;
        if(j==m) {
            ans++;
            j=0;
        }
    }
    return ans;
}
int main(){
    while(scanf(" %s",s+1)!=EOF){
        if(s[1] == '#') break;
        scanf(" %s",p+1);
        n=strlen(s+1),m=strlen(p+1);
        printf("%d\n",kmp());
    }
    return 0;
}