标签：扩展kmp   树状数组   

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5
xy
abc
aaa
aaaaba
aaxoaaaaa

0
0
1
1
2

题意其实就是要找到这个字符串的某个前缀, 它在串中至少出现了三次(末尾1次,中间一次, 开头一次)

那么我们可以用EKMP,先把next数组预处理出来(串和串本身的每一个后缀的最长公共前缀), 然后用树状数组维护大于等于next[i]的值的个数

显然符合的次数肯定大于等于3, 然后只要从后往前去找那些 i + next[i] == len 的 后缀(只有匹配到结束才说明存在某个前缀出现在后缀里),找一个最大值就行

复杂度O(nlogn)

/*************************************************************************
    > File Name: hdu4763.cpp
    > Author: ALex
    > Mail: zchao1995@gmail.com 
    > Created Time: 2015年02月02日 星期一 13时11分11秒
 ************************************************************************/

#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

const double pi = acos(-1);
const int inf = 0x3f3f3f3f;
const double eps = 1e-15;
typedef long long LL;
typedef pair <int, int> PLL;

const int N = 1000100;
char T[N];
int next[N];
int cnt_hash[N];
int tree[N];

int lowbit (int x)
{
	return x & (-x);
}

void add (int x)
{
	for (int i = x; i <= N; i += lowbit(i))
	{
		++tree[i];
	}
}

int sum (int x)
{
	int ans = 0;
	for (int i = x; i; i -= lowbit (i))
	{
		ans += tree[i];
	}
	return ans;
}

void EKMP ()
{
	int lent = strlen (T);
	next[0] = lent;
	int i, j, p, L;
	j = 0;
	while (j + 1 < lent && T[j] == T[j + 1])
	{
		++j;
	}
	next[1] = j;
	int a = 1;
	for (int i = 2; i < lent; ++i)
	{
		p = next[a] + a - 1;
		L = next[i - a];
		if (i + L < p + 1)
		{
			next[i] = L;
		}
		else
		{
			j = max (0, p - i + 1);
			while (i + j < lent && T[i + j] == T[j])
			{
				++j;
			}
			next[i] = j;
			a = i;
		}
	}
}

int main ()
{
	int t;
	scanf("%d", &t);
	while (t--)
	{
		memset (next, 0, sizeof(next));
		memset (tree, 0, sizeof(tree));
		scanf("%s", T);
		EKMP ();
		int len = strlen (T);
		int maxs = 0;
		int zero = 0;
		for (int i = 0; i < len; ++i)
		{
			if (next[i] == 0)
			{
				++zero;
				continue;
			}
			add (next[i]);
		}
		for (int i = len - 1; i >= 0; --i)
		{
			if (next[i] == 0)
			{
				continue;
			}
			if (i + next[i] - 1 != len - 1)
			{
				continue;
			}
			int cnt = len - sum (next[i] - 1) - zero;
			if (cnt >= 3)
			{
				maxs = max (maxs, next[i]);
			}
		}
		printf("%d\n", maxs);
	}
	return 0;
}

hdu4763---Theme Section

标签：扩展kmp   树状数组   

原文地址：http://blog.csdn.net/guard_mine/article/details/43407295