简介：
做hdu4300看到的题解，除了kmp还可以用字符串hash做
模板：
1 typedef unsigned long long ull;
2 const int maxn=100000+10;
3 const ull base = 163;
4 char s[maxn],t[maxn];
5 ull h1[maxn],h2[maxn];
6 ull p[maxn];
7 void init(){ ///处理hash值
8 p[0] = 1;
9 h1[0] = h2[0]=0;
10 int n = strlen(s+1); ///字符串从1开始读
11 for(int i = 1; i <=100000; i ++) p[i] =p[i-1] * base;
12 for(int i = 1; i <=n; i ++) hash[i] = hash[i - 1] * base + (s[i] - 'a');
13 }
14 ull geth(int l, int r, ull g[]){///取出g里l - r里面的字符串的hash值
15 return g[r] - g[l - 1] * p[r - l + 1];
16 }
字符串hash：
1 #include<bits/stdc++.h>
2 #define numm ch-48
3 #define pd putchar(' ')
4 #define pn putchar('\n')
5 #define pb push_back
6 #define debug(args...) cout<<#args<<"->"<<args<<endl
7 #define bug cout<<"************"
8 using namespace std;
9 template <typename T>
10 void read(T &res) {
11 bool flag=false;char ch;
12 while(!isdigit(ch=getchar())) (ch=='-')&&(flag=true);
13 for(res=numm;isdigit(ch=getchar());res=(res<<1)+(res<<3)+numm);
14 flag&&(res=-res);
15 }
16 template <typename T>
17 void write(T x) {
18 if(x<0) putchar('-'),x=-x;
19 if(x>9) write(x/10);
20 putchar(x%10+'0');
21 }
22 typedef long long ll;
23 typedef unsigned long long ull;
24 typedef long double ld;
25 const int maxn=100000+10;
26 const int maxm=1000+10;
27 const int inf=0x3f3f3f3f;
28 const int mod=1e9+7;
29 const ull base = 163;
30 char s[maxn],t[maxn];
31 ull h1[maxn],h2[maxn];
32 ull p[maxn];
33 void init(){ ///处理hash值
34 p[0] = 1;
35 h1[0] = h2[0]=0;
36 int n = strlen(s+1); ///字符串从1开始读
37 for(int i = 1; i <=100000; i ++) p[i] =p[i-1] * base;
38 // for(int i = 1; i <=n; i ++) hash[i] = hash[i - 1] * base + (s[i] - 'a');
39 }
40 ull geth(int l, int r, ull g[]){///取出g里l - r里面的字符串的hash值
41 return g[r] - g[l - 1] * p[r - l + 1];
42 }
43 int main()
44 {
45 init();
46 int _;
47 read(_);
48 char str[30];
49 while(_--) {
50 map<char,char>mp;
51 scanf("%s%s",str,s+1);
52 for(int i=0;i<26;i++)
53 mp[str[i]]=i+'a';
54 int lenstr=strlen(str),lens=strlen(s+1);
55 for(int i=1;i<=lens;i++)
56 t[i]=mp[s[i]];
57 for(int i=1;i<=lens;i++) {
58 h1[i]=h1[i-1]*base+(s[i]-'a');
59 h2[i]=h2[i-1]*base+(t[i]-'a');
60 }
61 int lent=strlen(t+1);
62 int a=lens/2+lens%2,pos=0;
63 for(int i=a;i<=lens;i++) {
64 int l=geth(1,lens-i,h2);
65 int r=geth(i+1,lens,h1);
66 if(l==r) {
67 pos=i;
68 break;
69 }
70 }
71 cout<<s+1;
72 if((pos<<1)!=lens) {
73 for(int i=lens-pos+1;i<=pos;i++)
74 putchar(t[i]);
75 }
76 pn;
77 }
78 return 0;
79 }
KMP：
1 #include<bits/stdc++.h>
2 #define numm ch-48
3 #define pd putchar(' ')
4 #define pn putchar('\n')
5 #define pb push_back
6 #define debug(args...) cout<<#args<<"->"<<args<<endl
7 #define bug cout<<"************"
8 using namespace std;
9 template <typename T>
10 void read(T &res) {
11 bool flag=false;char ch;
12 while(!isdigit(ch=getchar())) (ch=='-')&&(flag=true);
13 for(res=numm;isdigit(ch=getchar());res=(res<<1)+(res<<3)+numm);
14 flag&&(res=-res);
15 }
16 template <typename T>
17 void write(T x) {
18 if(x<0) putchar('-'),x=-x;
19 if(x>9) write(x/10);
20 putchar(x%10+'0');
21 }
22 typedef long long ll;
23 typedef long double ld;
24 const int maxn=100000+10;
25 const int maxm=1000+10;
26 const int inf=0x3f3f3f3f;
27 const int mod=1e9+7;
28 char s[maxn],t[maxn];
29 int net[maxn];
30 void getnext(char t[],int len) {
31 int i=0,j=-1;
32 net[0]=-1;
33 while(i<len) {
34 if(j==-1||t[i]==t[j]) {
35 i++,j++;
36 net[i]=j;
37 }
38 else j=net[j];
39 }
40 }
41 int KMP(int lens,int lent){
42 int j=0,i=lens/2+lens%2;
43 while(i<lens&&j<lent) {
44 if(j==-1||s[i]==t[j])
45 i++,j++;
46 else j=net[j];
47 }
48 return j;
49 }
50 int main()
51 {
52 int _;
53 read(_);
54 char str[30];
55 while(_--) {
56 map<char,char>mp;
57 scanf("%s%s",str,s);
58 for(int i=0;i<26;i++)
59 mp[str[i]]=i+'a';
60 int lenstr=strlen(str),lens=strlen(s);
61 for(int i=0;i<lens;i++)
62 t[i]=mp[s[i]];
63 int lent=strlen(t);
64 getnext(t,lent);
65 int len=KMP(lens,lent);
66 cout<<s;
67 if((len<<1)!=lenstr) {
68 for(int i=len;i<lens-len;i++)
69 putchar(t[i]);
70 }
71 pn;
72 }
73 return 0;
74 }