bzoj3555: [Ctsc2014]企鹅QQ （Hash）

枚举每个分段的点，每次O(n)更新左边和右边的hash值

然后用双指针O(n)计算答案

 1 #include<stdio.h>
 2 #include<string.h>
 3 #include<algorithm>
 4 #include<iostream>
 5 #define ull unsigned long long
 6 using namespace std;
 7 struct HS{
 8     ull l,r;
 9 }tmp[30010],hs[30010];
10 ull base,b[202],c[301];
11 int n,m;
12 char s[30010][203];
13
14 bool cmp(HS a, HS b){
15     if (a.l==b.l) return a.r<b.r; return a.l<b.l;
16 }
17
18 bool operator!=(HS a, HS b){
19     return ((a.l!=b.l) || (a.r!=b.r));
20 }
21
22 void pre(){
23     if (base==2) c[‘0‘]=1,c[‘1‘]=2;
24     else{
25         int cnt=0;
26         for (int i=‘A‘; i<=‘Z‘; i++) c[i]=++cnt;
27         for (int i=‘a‘; i<=‘z‘; i++) c[i]=++cnt;
28         for (int i=‘0‘; i<=‘9‘; i++) c[i]=++cnt;
29         c[‘_‘]=++cnt; c[‘@‘]=++cnt;
30     }
31     ++base; b[0]=1;
32     for (int i=1; i<=m; i++) b[i]=b[i-1]*base;
33 }
34
35 int main(){
36     scanf("%d%d", &n, &m); cin>>base;
37     pre();
38     for (int i=1; i<=n; i++){
39         scanf("%s", s[i]+1);
40         for (int j=2; j<=m; j++)
41             hs[i].r=hs[i].r*base+(ull)c[s[i][j]];
42     }
43     memcpy(tmp,hs,(n+1)*sizeof(HS));
44     ull ans=0LL;
45     for (int i=2; i<=m+1; i++){
46         int head=0;
47         sort(hs+1,hs+1+n,cmp);
48         for (int j=1; j<=n; j++){
49             tmp[j].l=tmp[j].l*base+c[s[j][i-1]];
50             tmp[j].r-=b[m-i]*c[s[j][i]];
51             if (j==1 || hs[j]!=hs[j-1]) head=j;
52             if (j==n || hs[j]!=hs[j+1]) ans+=(ull)(j-head)*(j-head+1)/2;
53         }
54         memcpy(hs,tmp,(n+1)*sizeof(HS));
55     }
56     cout<<ans<<endl;
57     return 0;
58 }