UVa719 Glass Bread(后缀数组解法)

题意:给出一个字符串，求其最小表示法

注意：用两个串拼成一个字符串，求其后缀数组及height数组

求其最小表示法时，过滤方法为

1、后缀数组的位置不能大于原字符串长度

2、其位置对应的height值不能小于字符串长度

代码如下：

#include 
#include 
#include 
#include 
#include 
#include 

using namespace std;

const int N = 256;

class SuffixArray
{
public:
	SuffixArray(string s);
	~SuffixArray();

	void buildSa();
	void getHeight();

	const int* getSa();
	const int* getH();
private:
	int *m_prank;
	int *m_pheight;
	int *m_psa;
	int m_n;
	string m_str;
};

SuffixArray::SuffixArray(std::string s)
	:m_prank(NULL), m_pheight(NULL), m_psa(NULL)
{
	m_str = s;
	m_n = m_str.length();
}

SuffixArray::~SuffixArray()
{
	delete[]m_prank;
	delete[]m_psa;
	delete[]m_pheight;
}

void SuffixArray::buildSa()
{
	m_prank = new int[m_n];
	int n = max(N, m_n);
	int* tmp = new int[m_n];
	int* c = new int[n];
	m_psa = new int[m_n];
	m_pheight = new int[m_n];

	memset(c, 0, sizeof(int) * n);
	for (int i = 0; i < m_n; i++)
	{
		m_prank[i] = m_str[i];
		c[m_prank[i]]++;
	}

	for (int i = 1; i < n; i++)
	{
		c[i] += c[i - 1];
	}

	for (int i = m_n - 1; i >= 0; i--)
	{
		m_psa[--c[m_prank[i]]] = i;
	}

	int m = m_n;
	for (int i = 1; i <= m_n; i <<= 1)
	{
		int p = 0;
		for (int j = m_n - i; j < m_n; j++)
		{
			tmp[p++] = j;
		}
		for (int j = 0; j < m_n; j++)
		{
			if (m_psa[j] >= i)
			{
				tmp[p++] = m_psa[j] - i;
			}
		}

		memset(c, 0, sizeof(int) * n);
		for (int j = 0; j < m_n; j++)
		{
			c[m_prank[tmp[j]]]++;
		}

		for (int j = 1; j < n; j++)
		{
			c[j] += c[j - 1];
		}


		for (int j = m_n - 1; j >= 0; j--)
		{
			m_psa[--c[m_prank[tmp[j]]]] = tmp[j];
		}

		swap(m_prank, tmp);

		m_prank[m_psa[0]] = 0;

		m = 0;
		for (int j = 1; j < m_n; j++)
		{
			if (tmp[m_psa[j - 1]] == tmp[m_psa[j]]
				&& m_psa[j - 1] + i < m_n
				&& m_psa[j] + i < m_n
				&& tmp[m_psa[j - 1] + i] == tmp[m_psa[j] + i])
			{
				m_prank[m_psa[j]] = m;
			}
			else
			{
				m_prank[m_psa[j]] = ++m;
			}
		}

		if (m >= m_n - 1) break;
	}

	delete[]c;
	delete[]tmp;

	return;
}

void SuffixArray::getHeight()
{
	m_pheight[0] = 0;

	int k = 0;
	for (int i = 0; i < m_n; i++)
	{
		int curPos = m_prank[i];
		if (curPos == 0) continue;
		curPos--;

		int j = m_psa[curPos];
		if (k)
		{
			k--;
		}
		while (i + k < m_n && j + k < m_n && m_str[i + k] == m_str[j + k]) k++;
		m_pheight[m_prank[i]] = k;
	}

	return;
}

const int* SuffixArray::getSa()
{
	return m_psa;
}

const int* SuffixArray::getH()
{
	return m_pheight;
}

int main(int argc, char **argv)
{
	int n;
	string s;

#ifndef ONLINE_JUDGE
	ifstream fin("f:\\OJ\\uva_in.txt");
	streambuf* old = cin.rdbuf(fin.rdbuf());
#endif

	cin >> n;
	while (n--)
	{
		cin >> s;
		string tmp = s;
		tmp += tmp;
		SuffixArray sa(tmp);
		sa.buildSa();
		sa.getHeight();

		const int* psa = sa.getSa();
		const int* pheight = sa.getH();
		int strLen = s.length();
		for (int i = 0; i < 2 * strLen; i++)
		{
			if (psa[i] < strLen)
			{
				int res = psa[i];
				while (i + 1 < 2 * strLen && pheight[i + 1] >= strLen)
				{
					i++;
					if (psa[i] < strLen)
					{
						res = min(res, psa[i]);
					}
					
				}
				cout << res + 1 << endl;
				break;
			}
		}
	}

#ifndef ONLINE_JUDGE
	cin.rdbuf(old);
	//cout.rdbuf(oldout);
#endif
}