KMP

#include <iostream>
#include <cstring>
using namespace std;
const int maxn = 1000000+7;
char s[maxn], p[maxn];
int net[maxn];
int lens, lenp;
void getnext() {
    net[0] = -1;
    int i = 0,j = -1;
    while (i < lenp - 1) {
        if (j == -1 || p[i] == p[j]) 
net[++i] = ++j;
        else j = net[j];
    }
}
int kmp() {
    lens = strlen(s);
    lenp = strlen(p);
    int i = 0, j = 0;
    getnext();
    while (i < lens && j < lenp) {
        if (s[i] == p[j] || j == -1) i++, j++;
        else j = net[j];
    }
    if (j == lenp) return i - j;
    else return -1;
}
int main() {
    cin >> s;
    cin >> p;
    int ans = kmp();
    cout << ans << endl;
    return 0;
}