manacher算法,在求p数组时多加个判断条件即可。
#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
const int maxn = 1e5+10;
int h[maxn],H[maxn],p[maxn];
int n;
int init()
{
H[0] = -1;
H[1] = 0;
int j = 2;
for(int i = 0; i < n; i++)
{
H[j++] = h[i];
H[j++] = 0;
}
H[j] = -3;
return j;
}
int manacher()
{
int len = init();
int id = 0,mx = 0;
int max_len = -1;
for(int i = 1; i < len; i++)
{
p[i] = mx > i ? min(p[2*id-i],mx-i):1;
while(H[i+p[i]] == H[i-p[i]] && (H[i-p[i]] == 0 || H[i-p[i]] <= H[i-p[i]+2]))//当H[i-p[i]]为插入字符或满足递增条件时,p[i]++
p[i]++;
if(i + p[i] > mx)
{
id = i;
mx = i + p[i];
}
max_len = max(max_len,p[i]-1);
}
return max_len;
}
int main()
{
int T;
scanf("%d",&T);
while(T--)
{
scanf("%d",&n);
for(int i = 0; i < n; i++)
scanf("%d",&h[i]);
printf("%d\n",manacher());
}
return 0;
}