poj 3974 Manacher Algorithm (求最长回文)

最新推荐文章于 2021-01-14 14:42:55 发布

原创最新推荐文章于 2021-01-14 14:42:55 发布 · 575 阅读

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本文深入探讨了Manacher算法的原理与实现细节，并通过POJ3974实例展示了其在解决字符串匹配问题上的高效性。算法核心在于利用回文串性质优化搜索过程，显著提升查找效率。

/*
    Subject: Manacher Algorithm
    Author : a_clay
    Created Date : 2011-12-26
    Sample : poj 3974
*/
#include <iostream>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <algorithm>
#define Bug cout << "here\n";

using namespace std;
const int N = 1000005;

char str1[N];
char str[2*N]; //start from index 1
int rad[2*N], nn, n;

void Manacher(int *rad, char *str, int n) { 
	int i, id = 0, mx = 0;
	for(i = 1; i < n; i++) {
		if(mx > i) {
			rad[i] = min(rad[2*id - i], mx - i);
		}
		else rad[i] = 1;

		while(str[i+rad[i]] == str[i-rad[i]]) rad[i]++;

		if(rad[i] + i > mx) {
			mx = i + rad[i];
			id = i;
		}
	}
}

int main() {
	int i, ans, ca = 0;
	while(cin >> str1, strcmp(str1, "END")) {
		nn = strlen(str1);
		n = 2*nn + 2;
		str[0] = '$';
		str[n] = '\0';
		for(i = 0; i <= nn; i++) {
			str[2*i + 1] = '#';
			if(i != nn) str[2*i + 2] = str1[i];
		}
		memset(rad, 0, sizeof(rad));
		Manacher(rad, str, n);
		ans = 1;
		for(i = 0; i < n; i++) {
			ans = max(rad[i], ans);
		}
		printf("Case %d: %d\n", ++ca, ans-1);
	}
	return 0;
}