KMP模板（洛谷P3375）

#include <bits/stdc++.h>
using namespace std;
string s1, s2;
vector<int> find_next(vector<int> next, string s)
{
    int i = 1, prefix = 0, len = s.length();
    while (i < len)
    {
        if (s[prefix] == s[i])
        {
            ++prefix, ++i;
            next.push_back(prefix);
        }
        else if (prefix == 0)
        {
            next.push_back(0);
            ++i;
        }
        else
            prefix = next[prefix - 1];
    }
    return next;
}
void kmp(vector<int> next, string s1, string s2)
{
    int len1 = s1.length(), len2 = s2.length();
    int i = 0, j = 0;
    while (i < len1)
    {
        while (j && s1[i] != s2[j])
            j = next[j - 1];
        if (s1[i] == s2[j])
            ++j;
        ++i;
        if (j == len2)
            cout << i - j + 1 << endl;
    }
}
int main()
{
    cin >> s1 >> s2;
    vector<int> next(1);
    next = find_next(next, s2);
    kmp(next, s1, s2);
    for (auto i : next)
        cout << i << " ";
}