KMP模板

nex数组：位置i的前缀子串的前缀与后缀最大相似值。

#include<bits/stdc++.h>
using namespace std;
typedef pair <int, int> pii;
#define mp make_pair
#define pb emplace_back
#define mt(a,b) memset(a,b,sizeof(a))
#define zero(x) (((x)>0?(x):-(x))<eps)
typedef long long ll;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int inf = 0x3f3f3f3f;
const double pi = 3.14159265;
const double eps = 0.000001;
const ll mod = 1e9 + 7;
const int maxn = 1e6 +7;

int nex[maxn];
char s[maxn], t[maxn];
int lt, ls;
int pos = 0;
void build_nex()
{
    nex[0] = 0;
    pos = 0;
    for(int i = 2; i <= lt; i ++)
    {
        while(pos && t[pos + 1] != t[i])
            pos = nex[pos];
        if(t[pos + 1] == t[i])
            pos ++;
        nex[i] = pos;
    }
}
void kmp()
{
    pos = 0;
    for(int i = 1; i <= ls; i ++)
    {
        while( pos && t[pos + 1] != s[i])
            pos = nex[pos];
        if(t[pos + 1] == s[i])
            pos ++;
        if(pos == lt)
        {
            printf("%d\n", i - lt + 1);
            pos = nex[pos];
        }
    }
}
int main()
{
    scanf("%s%s", s + 1, t + 1);
    lt = strlen(t + 1);
    ls = strlen(s + 1);
    
    build_nex();
    kmp();
    
    for(int i = 1; i <= lt; i ++)
    {
        printf("%d ", nex[i]);
    }
}
/*
3
1 2 2 1 2 2
*/