HDU-3294-Girls' research(Manacher)

链接:

http://acm.hdu.edu.cn/showproblem.php?pid=3294

题意:

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.

思路:

字符串的转换就是对每个字符, 偏移c-'a', c为给的字符,
然后跑马拉车, 算出在原串上的左端点,即可.

代码:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
//#include <memory.h>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <math.h>
#include <stack>
#include <string>
#include <assert.h>
#include <iomanip>
#include <iostream>
#include <sstream>
#define MINF 0x3f3f3f3f
using namespace std;
typedef long long LL;
const int MAXN = 4e5+10;

char a[MAXN], b[MAXN];
int Hw[MAXN];
int n;

void Manacher(char *ori)
{
    int len = strlen(ori);
    int maxr = 0, mid;
    for (int i = 1;i < len;i++)
    {
        if (i < maxr)
            Hw[i] = min(Hw[2*mid-i], maxr-i);
        else
            Hw[i] = 1;
        while (ori[i+Hw[i]] == ori[i-Hw[i]])
            Hw[i]++;
        if (i+Hw[i] < maxr)
        {
            maxr = i+Hw[i];
            mid = i;
        }
    }
}

void Change(char *ori, char *pet)
{
    int len = strlen(ori);
    pet[0] = pet[1] = '#';
    for (int i = 0;i < len;i++)
    {
        pet[2*i+2] = ori[i];
        pet[2*i+3] = '#';
    }
    pet[2*len+2] = 0;
}

int main()
{
    char c;
    while (~scanf("%c %s", &c, a))
    {
        getchar();
        int l = c-'a';
        int len = strlen(a);
        for (int i = 0;i < len;i++)
            a[i] = (a[i]-'a'-l+26)%26+'a';
        Change(a, b);
        Manacher(b);
        int p = 0;
        len = strlen(b);
        for (int i = 0;i < len;i++)
        {
            if (Hw[i] > Hw[p])
                p = i;
        }
        if (Hw[p]-1 < 2)
            puts("No solution!");
        else
        {
            int left = (p-Hw[p])/2;
            int right = left+Hw[p]-2;
            a[right+1] = 0;
            printf("%d %d
", left, right);
            printf("%s
", a+left);
        }
    }

    return 0;
}