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suffix_array.cpp
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62 lines (54 loc) · 1.66 KB
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/**
* 📑 Suffix Array (Simple O(N log^2 N) Implementation)
*
* A Suffix Array is a sorted array of all suffixes of a string.
* It is a foundational structure for many advanced string problems.
*/
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
/**
* Builds a suffix array in O(N log^2 N).
* p[i] is the starting index of the i-th lexicographically smallest suffix.
*/
vector<int> build_suffix_array(string s) {
s += "$"; // Add sentinel character
int n = s.size();
vector<int> p(n), c(n);
// k = 0
vector<pair<char, int>> a(n);
for (int i = 0; i < n; i++) a[i] = {s[i], i};
sort(a.begin(), a.end());
for (int i = 0; i < n; i++) p[i] = a[i].second;
c[p[0]] = 0;
for (int i = 1; i < n; i++) {
c[p[i]] = (a[i].first == a[i - 1].first) ? c[p[i - 1]] : c[p[i - 1]] + 1;
}
// Iterative sorting of doubled lengths
int k = 0;
while ((1 << k) < n) {
vector<pair<pair<int, int>, int>> b(n);
for (int i = 0; i < n; i++) {
b[i] = {{c[i], c[(i + (1 << k)) % n]}, i};
}
sort(b.begin(), b.end());
for (int i = 0; i < n; i++) p[i] = b[i].second;
c[p[0]] = 0;
for (int i = 1; i < n; i++) {
c[p[i]] = (b[i].first == b[i - 1].first) ? c[p[i - 1]] : c[p[i - 1]] + 1;
}
k++;
}
return p;
}
int main() {
string s = "banana";
vector<int> sa = build_suffix_array(s);
cout << "Suffix Array for '" << s << "':" << endl;
for (int i = 1; i < sa.size(); i++) { // Skip the '$' sentinel suffix
cout << sa[i] << ": " << s.substr(sa[i]) << endl;
}
return 0;
}