uva10829 L-Gap Substrings

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传送门：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=20&page=show_problem&problem=1770

思路：这题和上一题SPOJ687的思路一样，也是枚举长度，再对于i和i+j+L向前向后匹配，但是这一题只能在后面接一个反串。

#include<cmath>#include<cstdio>#include<cstring>#include<algorithm>const int maxn=100010;using namespace std;int n,sum[maxn],t1[maxn],t2[maxn],sa[maxn],rank[maxn],h[maxn],st[maxn][20],L,len;char s[maxn];long long ans;void getsa(){int *x=t1,*y=t2,m=255,p=0;for (int i=1;i<=n;i++) sum[x[i]=s[i]]++;for (int i=1;i<=m;i++) sum[i]+=sum[i-1];for (int i=n;i;i--) sa[sum[x[i]]--]=i;for (int j=1;p<n;j<<=1,m=p){p=0;for (int i=n-j+1;i<=n;i++) y[++p]=i;for (int i=1;i<=n;i++) if (sa[i]>j) y[++p]=sa[i]-j;memset(sum,0,sizeof(sum));for (int i=1;i<=n;i++) sum[x[y[i]]]++;for (int i=1;i<=m;i++) sum[i]+=sum[i-1];for (int i=n;i;i--) sa[sum[x[y[i]]]--]=y[i];swap(x,y),x[sa[1]]=p=1;for (int i=2;i<=n;i++){if (y[sa[i]]!=y[sa[i-1]]||y[sa[i]+j]!=y[sa[i-1]+j]) p++;x[sa[i]]=p;}}memcpy(rank,x,sizeof(rank));}void geth(){for (int i=1,j=0;i<=n;i++){if (rank[i]==1) continue;while (s[i+j]==s[sa[rank[i]-1]+j]) j++;h[rank[i]]=j;if (j) j--;}}void getst(){for (int i=1;i<=n;i++) st[i][0]=h[i];for (int j=1;j<=19;j++)for (int i=1;i+(1<<j)-1<=n;i++)st[i][j]=min(st[i][j-1],st[i+(1<<(j-1))][j-1]);}int getmin(int x,int y){int l=rank[x],r=rank[y];if (l>r) swap(l,r);l++;int k=log2(r-l+1);return min(st[l][k],st[r-(1<<k)+1][k]);}int main(){scanf("%d%s",&L,s+1);len=strlen(s+1),s[n=len+1]=127;for (int i=len;i;i--) s[++n]=s[i];s[n+1]=0;getsa(),geth(),getst();for (int i=1;i+i+L<=len;i++)for (int j=1;j<=len;j+=i){int k=j+i+L,tmp=0;if (k<=len) tmp+=min(i,getmin(j,k));if (j>=2) tmp+=min(i-1,getmin(n-j+2,n-k+2));ans+=max(0,tmp-i+1);}printf("%lld\n",ans);return 0;}

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