HDU 3294 (manachar)

Girls' research

Time Limit: 3000/1000 MS (Java/Others)    Memory Limit: 65535/32768 K (Java/Others)
Total Submission(s): 1520    Accepted Submission(s): 572

Problem Description

One day, sailormoon girls are so delighted that they intend to research about palindromic strings. Operation contains two steps:
First step: girls will write a long string (only contains lower case) on the paper. For example, "abcde", but 'a' inside is not the real 'a', that means if we define the 'b' is the real 'a', then we can infer that 'c' is the real 'b', 'd' is the real 'c' ……, 'a' is the real 'z'. According to this, string "abcde" changes to "bcdef".
Second step: girls will find out the longest palindromic string in the given string, the length of palindromic string must be equal or more than 2.

 

Input

Input contains multiple cases.
Each case contains two parts, a character and a string, they are separated by one space, the character representing the real 'a' is and the length of the string will not exceed 200000.All input must be lowercase.
If the length of string is len, it is marked from 0 to len-1.

 

Output

Please execute the operation following the two steps.
If you find one, output the start position and end position of palindromic string in a line, next line output the real palindromic string, or output "No solution!".
If there are several answers available, please choose the string which first appears.

 

Sample Input

   
   
   
   

    
    
    
    b babd
a abcd
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    0 2
aza
No solution!
   
   
   
   

 

题意:给出一个串和一个字符ch,这个串是原串把a替换成ch,b换成ch+1,c换成

ch+2..得来的,然后求原串的最长回文子序列.

manachar以后遍历一遍数组就好了,注意+26以后取模.

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>
using namespace std;
#define maxn 211111

int len[maxn<<1];
char s[maxn<<1];
char a[maxn];
char change;

int f (int x) {
    return (x-1)>>1;
}

int manachar (char *p) {
    int n = strlen (p), l = 0;
    s[l++] = '@';
    s[l++] = '#';
    for (int i = 0; i < n; i++) {
        s[l++] = p[i];
        s[l++] = '#';
    }
    s[l] = 0;

    int Max = 0, pos = 0, ans = 0;
    for (int i = 1; i < l; i++) {
        if (Max > i) {
            len[i] = min (len[2*pos-i], Max-i);
        }
        else
            len[i] = 1;
        while (s[i+len[i]] == s[i-len[i]])
            len[i]++;
        ans = max (ans, len[i]);
        if (len[i]+i > Max) {
            Max = len[i]+i;
            pos = i;
        }
    }
    ans--;
    if (ans == 1) {
        printf ("No solution!\n");
        return 0;
    }
    for (int i = 1; i < l; i++) {
        if (len[i]-1 == ans) {
            printf ("%d %d\n", f(i-len[i]+2), f(i+len[i]-2));
            for (int j = i-len[i]+1; j <= i+len[i]-1; j++) if (s[j] != '#') {
                printf ("%c", 'a'+(s[j]-change+26)%26);
            }
            puts ("");
            return 0;
        }
    }
    return 0;
}

int main () {
    //freopen ("in.txt", "r", stdin);
    while (scanf ("%s%s", s, a) == 2) {
        change = s[0];
        manachar (a);
    }
    return 0;
}