Search patterns within text using Suffix Array by utilizing C++ library functions

SuffixArray+Search-v2.cpp

/*====================================================================
 Title: Computes Longest Repeated Substring from a given string
 Complexity: O(n.log(n))
 Author : Sudipto Chandra (Dipu)
 =====================================================================*/
#include <bits/stdc++.h>
using namespace std;
#define mem(a,b) memset(a, b, sizeof(a))
#define loop(i, x) for(__typeof((x).begin()) i=(x).begin(); i!=(x).end(); ++i)
#define rloop(i, x) for(__typeof((x).rbegin()) i=(x).rbegin(); i!=(x).rend(); ++i)
/*------------------------------------------------------------------------------------*/

int test, cas = 1;

const int SIZ = 10000050; // maximum possible size

int n; // text length
int m; // pattern length
char T[SIZ]; // text
char P[SIZ]; // pattern
int SA[SIZ], tempSA[SIZ]; // the sorted suffixes
int RA[SIZ], tempRA[SIZ]; // ranks of suffix array
int L[SIZ]; // used in counting sort

inline int getRA(int i)
{
    return (i < n) ? RA[i] : 0;
}

void radix_sort(int k)
{
    mem(L, 0);
    // count frequencies
    for(int i = 0; i < n; ++i)
    {
        L[getRA(i + k)]++;
    }
    // save first index of every characters
    int mx = max(n, 130);
    for(int i = 0, s = 0; i < mx; ++i)
    {
        int x = L[i];
        L[i] = s;
        s += x;
    }
    // build sorted tempSA
    for(int i = 0; i < n; ++i)
    {
        int& x = L[getRA(SA[i] + k)];
        tempSA[x++] = SA[i];
    }
    // copy tempSA to SA
    for(int i = 0; i < n; ++i)
    {
        SA[i] = tempSA[i];
    }
}
// text must ends with a $
void buildSA()
{
    // initialize
    n = strlen(T);
    T[n++] = '$', T[n] = 0; // append $
    for(int i = 0; i < n; ++i)
    {
        SA[i] = i;
        RA[i] = T[i];
    }

    // algorithm loop
    for(int k = 1; k < n; k <<= 1)
    {
        // sort by k-th ranks
        radix_sort(k);
        radix_sort(0);
        // compute new ranks
        tempRA[SA[0]] = 0;
        for(int i = 1, r = 0; i < n; ++i)
        {
            if(getRA(SA[i-1]) != getRA(SA[i])) {
                r++;
            }
            else if(getRA(SA[i-1]+k) != getRA(SA[i]+k)) {
                r++;
            }
            tempRA[SA[i]] = r;
        }
        for(int i = 0; i < n; ++i)
        {
            RA[i] = tempRA[i];
        }
        if(RA[SA[n - 1]] == n - 1) break;
    }
}

// functions used to count occurrences of pattern
bool isLesser(int t, const char* p)
{
    return strncmp(T + t, p, m) < 0;
}
bool isGreater(const char* p, int t)
{
    return strncmp(T + t, p, m) > 0;
}

// Count the number of times a given pattern P appears
// in the string T. Complexity: O(n.log(n))
int countOccurrences()
{
    m = strlen(P);

    int first = lower_bound(SA, SA + n, P, isLesser) - SA;
    int last = upper_bound(SA, SA + n, P, isGreater) - SA;

    printf("%d %d\n", first, last);
    return last - first;
}

int main()
{
    /*
        GATAGACA
        GA

        abcabxabcd
        abc

        mississippi
        i
    */

    printf("Text: ");
    scanf("%s", T);
    printf("Pattern: ");
    scanf("%s", P);

    buildSA();

    for(int i = 0; i < n; ++i)
    {
        printf("%2d | %2d | %s\n", i, SA[i], T + SA[i]);
    }

    int ans = countOccurrences();

    printf("Pattern found %d times\n", ans);

    return 0;
}