manacher算法 洛谷3805 manacher

Description

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给出一个只由小写英文字符a,b,c…y,z组成的字符串S,求S中最长回文串的长度.

字符串长度为n

Input

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一行小写英文字符a,b,c…y,z组成的字符串S

Output

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一个整数表示答案

Data Constraint

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字符串长度len <= 11000000

Solution

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manacher裸题，纯粹找手感

Code

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#include <stdio.h>#include <string.h>#define rep(i, st, ed) for (int i = st; i <= ed; i += 1)#define min(x, y) (x)<(y)?(x):(y)#define max(x, y) (x)>(y)?(x):(y)#define L 22000003int rad[L];char rd[L], str[L];int main(void){    scanf("%s", rd);    int len = strlen(rd);    str[0] = '#';    rep(i, 0, len - 1){        str[i * 2 + 1] = rd[i];        str[i * 2 + 2] = '#';    }    len = len * 2 + 1;    int pos = 0, mx = 0;    int ans = 0;    rep(i, 0, len){        rad[i] = 0;        if (i < mx){            rad[i] = min(rad[pos - (i - pos)], mx - i);        }        while (i + rad[i] + 1 < len && i - rad[i] > && str[i + rad[i] + 1] == str[i - rad[i] - 1]){            rad[i] += 1;        }        if (rad[i] + i > mx){            mx = rad[i] + i;            pos = i;        }        ans = max(ans, rad[i]);    }    printf("%d\n", ans);    return 0;}