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：

 1 #include <set>
 2 #include <map>
 3 #include <queue>
 4 #include <stack>
 5 #include <cmath>
 6 #include <bitset>
 7 #include <cstdio>
 8 #include <string>
 9 #include <vector>
10 #include <cstdlib>
11 #include <cstring>
12 #include <iostream>
13 #include <algorithm>
14 using namespace std;
15 
16 typedef long long ll;
17 typedef pair<ll, ll> pll;
18 typedef pair<ll, int> pli;
19 typedef pair<int, ll> pil;;
20 typedef pair<int, int> pii;
21 typedef unsigned long long ull;
22 
23 #define lson i<<1
24 #define rson i<<1|1
25 #define bug printf("*********\n");
26 #define FIN freopen("D://code//in.txt", "r", stdin);
27 #define debug(x) cout<<"["<<x<<"]" <<endl;
28 #define IO ios::sync_with_stdio(false),cin.tie(0);
29 
30 const double eps = 1e-8;
31 const int mod = 10007;
32 const int maxn = 1e6 + 7;
33 const double pi = acos(-1);
34 const int inf = 0x3f3f3f3f;
35 const ll INF = 0x3f3f3f3f3f3f3f;
36 
37 int lens1, lens2;
38 string s1, s2;
39 int nex[maxn];
40 
41 void get_next() {
42     nex[0] = -1;
43     for(int i = 0, k = -1; i < lens2; ) {
44         if(k == -1 || s2[i] == s2[k]) {
45             ++k;++i;
46             nex[i] = k;
47         } else k = nex[k];
48     }
49 }
50 
51 void kmp() {
52     get_next();
53     int i = 0, j = 0;
54     while(i < lens1 && j < lens2) {
55         if(j == -1 || s1[i] == s2[j]) {
56             i++,j++;
57             if(j == lens2) {
58                 printf("%d\n", i - j + 1);
59                 j = nex[j];
60             }
61         } else j = nex[j];
62     }
63 }
64 
65 int main() {
66     //FIN;
67     cin >>s1 >>s2;
68     lens1 = s1.size(), lens2 = s2.size();
69     kmp();
70     for(int i = 1; i <= lens2; i++) {
71         printf("%d%c", nex[i], i == lens2 ? '\n' : ' ');
72     }
73     return 0;
74 }