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/** | ||
* @file duval.cpp | ||
* @brief Implementation of [Duval's algorithm](https://en.wikipedia.org/wiki/Lyndon_word). | ||
* | ||
* @details | ||
* Duval's algorithm is an algorithm to find the lexicographically smallest | ||
* rotation of a string. It is based on the concept of Lyndon words. | ||
* Lyndon words are defined as the lexicographically smallest string in a | ||
* rotation equivalence class. A rotation equivalence class is a set of strings | ||
* that can be obtained by rotating a string. For example, the rotation | ||
* equivalence class of "abc" is {"abc", "bca", "cab"}. The lexicographically | ||
* smallest string in this class is "abc". | ||
* | ||
* Duval's algorithm works by iterating over the string and finding the | ||
* smallest rotation of the string that is a Lyndon word. This is done by | ||
* comparing the string with its suffixes and finding the smallest suffix that | ||
* is lexicographically smaller than the string. This suffix is then added to | ||
* the result and the process is repeated with the remaining string. | ||
* The algorithm has a time complexity of O(n) where n is the length of the | ||
* string. | ||
* | ||
* @note While Lyndon words are described in the context of strings, | ||
* Duval's algorithm can be used to find the lexicographically smallest cyclic | ||
* shift of any sequence of comparable elements. | ||
* | ||
* @author [Amine Ghoussaini](https://github.com/aminegh20) | ||
*/ | ||
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#include <array> /// for std::array | ||
#include <cassert> /// for assert | ||
#include <cstddef> /// for std::size_t | ||
#include <deque> /// for std::deque | ||
#include <iostream> /// for std::cout and std::endl | ||
#include <string> /// for std::string | ||
#include <vector> /// for std::vector | ||
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/** | ||
* @brief string manipulation algorithms | ||
* @namespace | ||
*/ | ||
namespace string { | ||
/** | ||
* @brief Find the lexicographically smallest cyclic shift of a sequence. | ||
* @tparam T type of the sequence | ||
* @param s the sequence | ||
* @returns the 0-indexed position of the least cyclic shift of the sequence | ||
*/ | ||
template <typename T> | ||
size_t duval(const T& s) { | ||
size_t n = s.size(); | ||
size_t i = 0, ans = 0; | ||
while (i < n) { | ||
ans = i; | ||
size_t j = i + 1, k = i; | ||
while (j < (n + n) && s[j % n] >= s[k % n]) { | ||
if (s[k % n] < s[j % n]) { | ||
k = i; | ||
} else { | ||
k++; | ||
} | ||
j++; | ||
} | ||
while (i <= k) { | ||
i += j - k; | ||
} | ||
} | ||
return ans; | ||
// returns 0-indexed position of the least cyclic shift | ||
} | ||
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} // namespace string | ||
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/** | ||
* @brief self test implementation | ||
* returns void | ||
*/ | ||
static void test() { | ||
using namespace string; | ||
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// Test 1 | ||
std::string s1 = "abcab"; | ||
assert(duval(s1) == 3); | ||
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// Test 2 | ||
std::string s2 = "011100"; | ||
assert(duval(s2) == 4); | ||
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// Test 3 | ||
std::vector<int> v = {5, 2, 1, 3, 4}; | ||
assert(duval(v) == 2); | ||
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// Test 4 | ||
std::array<int, 5> a = {1, 2, 3, 4, 5}; | ||
assert(duval(a) == 0); | ||
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// Test 5 | ||
std::deque<char> d = {'a', 'z', 'c', 'a', 'b'}; | ||
assert(duval(d) == 3); | ||
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// Test 6 | ||
std::string s3; | ||
assert(duval(s3) == 0); | ||
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// Test 7 | ||
std::vector<int> v2 = {5, 2, 1, 3, -4}; | ||
assert(duval(v2) == 4); | ||
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std::cout << "All tests passed!" << std::endl; | ||
} | ||
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/** | ||
* @brief main function | ||
* @returns 0 on exit | ||
*/ | ||
int main() { | ||
test(); // run self test implementations | ||
return 0; | ||
} |