hdu 4513 吉哥系列故事——完美队形II Manacher变形

AC CODE

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int MX = 1e5 + 5;
int A[MX];
int ma[MX<<1];
int p[MX<<1];

void Manacher(int n)
{
int l = 0;
ma[l++] = -2;
ma[l++] = 0;
for(int i=0;i<n;i++) {
ma[l++] = A[i];
ma[l++] = 0;
}
ma[l] = -3;p[0] = 0;
int mx = 0,id = 0;
for(int i=0;i<=l;i++) {
p[i] = mx>i ? min(p[2*id-i],mx-i) : 1;
while(ma[i+p[i]] == ma[i-p[i]] && ma[i-p[i]]<=ma[i-p[i]+2]) p[i]++;
if(i+p[i]>mx) {
mx = i+p[i];
id = i;
}
}

}

int main()
{
int _,n;//freopen("in.txt","r",stdin);
scanf("%d",&_);
while(_--)
{
scanf("%d",&n);
for(int i=0;i<n;i++) scanf("%d",&A[i]);
Manacher(n);
int ans = 0;
for(int i=1;i<=2*n+1;i++) ans = max(ans,p[i]-1);
printf("%d\n",ans);
}

return 0;
}