C++ Programming Code Examples
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C++ Program to Implement Suffix Tree
/* C++ Program to Implement Suffix Tree
This C++ Program demonstrates the implementation of Suffix Tree. */
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <string>
using namespace std;
typedef unsigned char byte;
/* SuffixNode Declaration */
class SuffixNode
{
public:
int depth, begin, end;
SuffixNode **children;
SuffixNode *parent, *suffixLink;
/* Constructor */
SuffixNode(int begin, int end, int depth, SuffixNode *parent)
{
children = new SuffixNode* [38];
this->begin = begin;
this->end = end;
this->parent = parent;
this->depth = depth;
}
bool contains(int d)
{
return depth <= d && d < depth + (end - begin);
}
};
string alphabet;
int alphabetSize;
int lcsLength;
int lcsBeginIndex;
/* Class SuffixTree Declaration */
class SuffixTree
{
public:
/* Funtion to build suffix tree for given text */
SuffixNode *buildSuffixTree(string s)
{
int n = s.length();
int *a = new int[n];
for (int i = 0; i < n; i++)
{
a[i] = alphabet.find(s.at(i));
}
SuffixNode *root = new SuffixNode(0, 0, 0, NULL);
SuffixNode *cn = root;
root->suffixLink = root;
SuffixNode *needsSuffixLink = NULL;
int lastRule = 0;
int j = 0;
for (int i = -1; i < n - 1; i++)
{
int cur = a[i + 1];
for (; j <= i + 1; j++)
{
int curDepth = i + 1 - j;
if (lastRule != 3)
{
if (cn->suffixLink != NULL)
cn = cn->suffixLink;
else
cn = cn->parent->suffixLink;
int k = j + cn->depth;
while (curDepth > 0 && !cn->contains(curDepth - 1))
{
k += cn->end - cn->begin;
cn = cn->children[a[k]];
}
}
if (!cn->contains(curDepth))
{
if (needsSuffixLink != NULL)
{
needsSuffixLink->suffixLink = cn;
needsSuffixLink = NULL;
}
if (cn->children[cur] == NULL)
{
cn->children[cur] = new SuffixNode(i + 1, n, curDepth, cn);
lastRule = 2;
}
else
{
cn = cn->children[cur];
lastRule = 3;
break;
}
}
else
{
int end = cn->begin + curDepth - cn->depth;
if (a[end] != cur)
{
SuffixNode *newn = new SuffixNode(cn->begin, end, cn->depth, cn->parent);
newn->children[cur] = new SuffixNode(i + 1, n, curDepth, newn);
newn->children[a[end]] = cn;
cn->parent->children[a[cn->begin]] = newn;
if (needsSuffixLink != NULL)
needsSuffixLink->suffixLink = newn;
cn->begin = end;
cn->depth = curDepth;
cn->parent = newn;
cn = needsSuffixLink = newn;
lastRule = 2;
}
else if (cn->end != n || (cn->begin - cn->depth) < j)
{
lastRule = 3;
break;
}
else
lastRule = 1;
}
}
}
root->suffixLink = NULL;
return root;
}
/* Funtion to find longest common substring */
int findLCS(SuffixNode *node, int i1, int i2)
{
if (node->begin <= i1 && i1 < node->end)
return 1;
if (node->begin <= i2 && i2 < node->end)
return 2;
int mask = 0;
for (int f = 0; f < alphabetSize; f++)
{
if (node->children[f] != NULL)
{
mask |= findLCS(node->children[f], i1, i2);
}
}
if (mask == 3)
{
int curLength = node->depth + node->end - node->begin;
if (lcsLength < curLength)
{
lcsLength = curLength;
lcsBeginIndex = node->begin;
}
}
return mask;
}
/* Funtion to find longest common substring */
void findLCS(string s1, string s2)
{
string x = "-";
string y = "#";
string ns1 = s1;
string ns2 = s2;
string s = s1.append(x.append(s2.append(y)));
SuffixNode *root = buildSuffixTree(s);
lcsLength = 0;
lcsBeginIndex = 0;
findLCS(root, ns1.length(), ns1.length() + ns2.length() + 1);
bool chk = lcsLength > 0;
if (chk)
{
cout<<"\nLongest substring is "<<s.substr(lcsBeginIndex , lcsLength);
cout<<endl;
}
else
{
cout<<"No substring found"<<endl;
}
}
};
/* Main */
int main()
{
alphabet = "abcdefghijklmnopqrstuvwxyz1234567890-#";
alphabetSize = alphabet.length();
string s1,s2;
cout<<"Finding longest common substring using suffix trees\n";
cout<<"Enter 1st String: ";
cin>>s1;
cout<<"Enter 2nd String: ";
cin>>s2;
SuffixTree st;
st.findLCS(s1, s2);
return 0;
}
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