洛谷 P3375 【模板】KMP字符串匹配

我这段时间因为字符串太差而被关了起来了（昨晚打cf不会处理字符串现场找大佬模板瞎搞，差点就凉了），所以决定好好补一下字符串的知识QAQ，暂时先学习kmp算法吧~

题目链接：https://www.luogu.org/problemnew/show/P3375

题目：

思路：本题是kmp模板题，不会kmp的看官可以看本题在洛谷的题解，题解区有大量的讲解，我顺便在这里推荐一篇大佬的文章，帮助大家理解kmp算法，http://www.ruanyifeng.com/blog/2013/05/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm.html。

代码实现如下：

#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cmath>
#include <bitset>
#include <cstdio>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<ll, int> pli;
typedef pair<int, ll> pil;;
typedef pair<int, int> pii;
typedef unsigned long long ull;

#define lson i<<1
#define rson i<<1|1
#define bug printf("*********
");
#define FIN freopen("D://code//in.txt", "r", stdin);
#define debug(x) cout<<"["<<x<<"]" <<endl;
#define IO ios::sync_with_stdio(false),cin.tie(0);

const double eps = 1e-8;
const int mod = 10007;
const int maxn = 1e6 + 7;
const double pi = acos(-1);
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f;

int lens1, lens2;
string s1, s2;
int nex[maxn];

void get_next() {
    nex[0] = -1;
    for(int i = 0, k = -1; i < lens2; ) {
        if(k == -1 || s2[i] == s2[k]) {
            ++k;++i;
            nex[i] = k;
        } else k = nex[k];
    }
}

void kmp() {
    get_next();
    int i = 0, j = 0;
    while(i < lens1 && j < lens2) {
        if(j == -1 || s1[i] == s2[j]) {
            i++,j++;
            if(j == lens2) {
                printf("%d
", i - j + 1);
                j = nex[j];
            }
        } else j = nex[j];
    }
}

int main() {
    //FIN;
    cin >>s1 >>s2;
    lens1 = s1.size(), lens2 = s2.size();
    kmp();
    for(int i = 1; i <= lens2; i++) {
        printf("%d%c", nex[i], i == lens2 ? '
' : ' ');
    }
    return 0;
}