题目传送门:https://vjudge.net/problem/HDU-3294
就是manacher求一下回文串,同时记录一下起始位置和长度,输出。先进行字母的替换。
感觉,最不好推得是,根据变形后的字符串去找现在字符串的位置。
l = (i - 1)/2 - (ans - 1)/2;
r = l + ans - 2;
ac代码:
#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cctype>
#include <string>
#include <vector>
#include <queue>
#include <cmath>
#include <stack>
#include <map>
#include <set>
#define N 200005
#define ll long long
using namespace std;
char a[N];
char s[2*N];
int p[2*N], len, l, r;
int manacher()
{
int pos = 0, maxr = 0, ans = 0;
for(int i = 2; i <= 2*len; i++)
{
p[i] = i < maxr ? min(p[2*pos-i], maxr -i) : 1;
while(s[i+p[i]] == s[i-p[i]])
p[i]++;
if(i + p[i] > maxr)
maxr = i + p[i], pos = i;
if(ans < p[i])
{
ans = p[i];
l = (i - 1)/2 - (ans - 1)/2;
r = l + ans - 2;
}
}
return ans - 1;
}
int main()
{
char ch;
while(scanf("%c %s%*c", &ch, a+1)!=EOF)
{
len = strlen(a+1);
s[0] = '$';
s[1] = '#';
int c = ch;
for(int i = 1; i <= len; i++)
{
s[i*2+1] = '#';
int b = a[i];
s[i*2] = abs(b - c + 26) % 26 + 'a';
}
int ans = manacher();
if(ans <= 1)
{
printf("No solution!\n");
}
else
{
printf("%d %d\n", l, r);
for(int i = l+1; i <= r+1; i++)
{
int b = a[i];
printf("%c", abs(b - c + 26) % 26 + 'a');
}
printf("\n");
}
}
return 0;
}