题目大意:RT
分析:后缀数组求回文串,不得不说确实比较麻烦,尤其是再用线段数进行查询,需要注意的细节地方比较多,比赛实用性不高......不过练练手还是可以的。
线段数+后缀数组代码如下:
===========================================================================================================================================
#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std; const int MAXN = 1e4+; struct SuffixArr
{
int tempx[MAXN], tempy[MAXN], text[MAXN];
int rank[MAXN], sa[MAXN], height[MAXN], sum[MAXN];
int *x, *y, N, MaxId; void GetText(char s[])
{
N = strlen(s)*+, MaxId = ;
x = tempx, y = tempy;
int i;
for(i=; s[i]; i++)
{
text[i] = text[N-i-] = x[i] = x[N-i-] = (int)s[i];
y[i] = i, y[N-i-] = N-i-;
} text[i] = x[i] = , y[i] = i;
text[N-] = x[N-] = , y[N-] = N-; /// debug();
}
bool cmp(int i, int len)
{
if(sa[i]+len > N || sa[i-]+len > N)
return false;
if(y[sa[i]] != y[sa[i-]] || y[sa[i]+len] != y[sa[i-]+len])
return false; return true;
}
void baseSort()
{
for(int i=; i<MaxId; i++)
sum[i] = ;
for(int i=; i<N; i++)
sum[ x[ y[i] ] ] += ;
for(int i=; i<MaxId; i++)
sum[i] += sum[i-];
for(int i=N-; i>=; i--)
sa[ --sum[ x[ y[i] ] ] ] = y[i];
}
void GetSa()
{
baseSort(); for(int len=; len<=N; len<<=)
{
int id = ; for(int i=N-len; i<N; i++)
y[id++] = i;
for(int i=; i<N; i++)if(sa[i] >= len)
y[id++] = sa[i] - len; baseSort();
swap(x, y);
x[ sa[] ] = id = ; for(int i=; i<N; i++)
{
if(cmp(i, len) == true)
x[ sa[i] ] = id;
else
x[ sa[i] ] = ++id;
} MaxId = id + ; if(MaxId >= N)break;
}
}
void GetHeight()
{
for(int i=; i<N; i++)
rank[ sa[i] ] = i; for(int k=, i=; i<N; i++)
{
if(!rank[i])
{
height[] = k = ;
continue;
}
if(k)k--; int pre = sa[ rank[i]- ]; while(text[i+k] == text[pre+k])
k++;
height[rank[i]] = k;
}
/// debug();
} void debug()
{
for(int i=; i<N; i++)
printf("%d: %d\n", i, height[i]);
}
};
struct segmentTree
{
int val[MAXN], L[MAXN], R[MAXN]; void Build(int root, int l, int r, int p[])
{
L[root] = l, R[root] = r; if(l == r)
{
val[root] = p[l];
return ;
} int Mid = (l+r)>>; Build(root<<, l, Mid, p);
Build(root<<|, Mid+, r, p); val[root] = min(val[root<<], val[root<<|]);
}
int Query(int root, int u, int v)
{ if(L[root] == u && R[root] == v)
return val[root]; int Mid = (L[root]+R[root]) / ; if(v <= Mid)
return Query(root<<, u, v);
else if(u > Mid)
return Query(root<<|, u, v);
else
return min(Query(root<<, u, Mid), Query(root<<|, Mid+, v));
}
}; SuffixArr suf;
segmentTree seg;
char s[MAXN]; int main()
{
while(scanf("%s", s) != EOF)
{
int len = strlen(s)+; suf.GetText(s);
suf.GetSa();
suf.GetHeight(); seg.Build(, , suf.N-, suf.height); int MaxLen=, k=, x, y; for(int i=; i<len-; i++)
for(int j=; j<; j++)
{
if(j==)
x = suf.rank[len*-i-];
else
x = suf.rank[len*-i-]; if(i== && j)continue; y = suf.rank[i+]; if(x > y)swap(x, y); int m = seg.Query(, x+, y) * + j; if(MaxLen < m)
{
MaxLen = m;
k = i-(m+j)/+;
}
} s[k+MaxLen] = ; printf("%s\n", s+k);
} return ;
}