# 【BZOJ 3676】[Apio2014]回文串

【链接】 链接
【题意】

【题解】

【错的次数】

【反思】

【代码】

#include<bits/stdc++.h>
using namespace std;

const int N = 3e5;
const int MAX_CHAR = 255;//每个数字的最大值。
char s[N + 10];//如果是数字,就写成int s[N+10]就好,从0开始存
int Sa[N + 10], T1[N + 10], T2[N + 10], C[N+10];
int Height[N + 10], Rank[N + 10];

void build_Sa(int n, int m) {
int i, *x = T1, *y = T2;
for (i = 0; i<m; i++) C[i] = 0;
for (i = 0; i<n; i++) C[x[i] = s[i]]++;
for (i = 1; i<m; i++) C[i] += C[i - 1];
for (i = n - 1; i >= 0; i--) Sa[--C[x[i]]] = i;
for (int k = 1; k <= n; k <<= 1)
{
int p = 0;
for (i = n - k; i<n; i++) y[p++] = i;
for (i = 0; i<n; i++) if (Sa[i] >= k) y[p++] = Sa[i] - k;
for (i = 0; i<m; i++) C[i] = 0;
for (i = 0; i<n; i++) C[x[y[i]]]++;
for (i = 1; i<m; i++) C[i] += C[i - 1];
for (i = n - 1; i >= 0; i--) Sa[--C[x[y[i]]]] = y[i];
swap(x, y);
p = 1; x[Sa[0]] = 0;
for (i = 1; i<n; i++)
x[Sa[i]] = y[Sa[i - 1]] == y[Sa[i]] && y[Sa[i - 1] + k] == y[Sa[i] + k] ? p - 1 : p++;
if (p >= n) break;
m = p;
}
}

void getHeight(int n)
{
int i, j, k = 0;
for (i = 1; i <= n; i++) Rank[Sa[i]] = i;
for (i = 0; i<n; i++) {
if (k) k--;
j = Sa[Rank[i] - 1];
while (s[i + k] == s[j + k]) k++;
Height[Rank[i]] = k;
}
}

const int MAXL = 19;//log2数组的最大长度
const int INF = 0x3f3f3f3f;//数值绝对值的最大值

struct abc{
int pre2[MAXL+5],need[N+10];
int fmin[N+10][MAXL+5];

void init(int n)
{
pre2[0] = 1;
for (int i = 1;i <= MAXL;i++)
{
pre2[i] = pre2[i-1]<<1;
}
need[1] = 0; need[2] = 1;
int temp = 2;
for (int i = 3; i <= n; i++)//need[i]表示长度为i是2的多少次方,可以理解为[log2i]
if (pre2[temp] == i)
need[i] = need[i - 1] + 1, temp++;
else
need[i] = need[i - 1];
}

void getst(int *a,int n)
{
memset(fmin,INF,sizeof fmin);
for (int i = 1;i <= n;i++)//下标从0开始就改成对应的就好
fmin[i][0] = a[i];

for (int l = 1;pre2[l]<=n;l++)
for (int i = 1;i <= n;i++)
if (i+pre2[l]-1<=n)
fmin[i][l] = min(fmin[i][l-1],fmin[i+pre2[l-1]][l-1]);
}

int getmin(int l,int r)
{
int len = need[r-l+1];
return min(fmin[l][len],fmin[r-pre2[len]+1][len]);
}

}ST;

char S[2*N+100];
int belong[2*N+100],p[2*N+100];
int n;
long long ans = 0;

int lcp(int x,int y)
{
return ST.getmin(x+1,y);
}

void cal(int x,int y)
{
int len = y - x + 1;//子串s[x..y]的长度
int temp = Rank[x];//这个后缀x的排名

int pr = temp;//最右能到哪里
int l = temp+1,r = n;
while (l <= r)
{
int mid = (l+r)>>1;
if (lcp(temp,mid)>=len)
{
pr = mid;
l = mid + 1;
}else
r = mid - 1;
}
int pl = temp;
l = 1,r = temp - 1;
while (l <= r)
{
int mid = (l+r)>>1;
if (lcp(mid,temp)>=len)
{
pl = mid;
r = mid - 1;
}else
l = mid + 1;
}
ans = max(ans,1LL*(pr-pl+1)*len);
}

int main() {
//freopen("F:\\rush.txt","r",stdin);
scanf("%s", s);
n = strlen(s);

s[n] = 0;
build_Sa(n + 1, MAX_CHAR);//注意调用n+1
getHeight(n);
ST.init(n);
ST.getst(Height,n);

int len = 0;
S[len++] = '\$';
S[len++] = '#';
for (int i = 0;i < n;i++)
{
S[len++] = s[i];
belong[len-1] = i;
S[len++] = '#';
}

int mx = 0,id = 0;
for (int i = 1;i < len;i++)
{
if (i > mx)
p[i] = 1;
else
p[i] = min(p[2*id-i],mx-i+1);
while (S[i-p[i]]==S[i+p[i]])
{
if (i+p[i] > mx && S[i-p[i]+1]!='#')
{
cal(belong[i-p[i]+1],belong[i+p[i]-1]);
}
p[i]++;
}
if (i + p[i]-1 > mx) mx = i + p[i] - 1,id = i;
}
printf("%lld\n",ans);
return 0;
}


posted @ 2017-10-06 15:14  AWCXV  阅读(193)  评论(0编辑  收藏  举报