对板子的详细解释见：pecco:kmp

板子

void get_pmt(const string& p) {//求pmt数组for (int i = 1, j = 0;i < p.size();i++) {while (j && p[i] != p[j])j = pmt[j - 1];if (p[i] == p[j])j++;pmt[i] = j;}
}void kmp(const string& s, const string& p) {//kmp算法for (int i = 0, j = 0;i < s.size();i++) {while (j && s[i] != p[j])j = pmt[j - 1];if (s[i] == p[j])j++;if (j == p.size()) {cout << i - j + 2 << '\n';j = pmt[j - 1];}}
}

注

pmt数组含义：截图来自peccp的文章kmp算法

例题

洛谷p3375kmp模板

#include<bits/stdc++.h>using namespace std;const int M = 1e6 + 9;
int pmt[M];void get_pmt(const string& p) {for (int i = 1, j = 0;i < p.size();i++) {while (j && p[i] != p[j])j = pmt[j - 1];if (p[i] == p[j])j++;pmt[i] = j;}
}void kmp(const string& s, const string& p) {for (int i = 0, j = 0;i < s.size();i++) {while (j && s[i] != p[j])j = pmt[j - 1];if (s[i] == p[j])j++;if (j == p.size()) {cout << i - j + 2 << '\n';j = pmt[j - 1];}}
}int main()
{ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);string s, p;cin >> s >> p;get_pmt(p);kmp(s, p);for (int i = 0;i < p.size();i++)cout << pmt[i] << ' ';return 0;
}