113 lines
2.3 KiB
C++
113 lines
2.3 KiB
C++
/* qsort.cpp
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* Date: 2024-06-22
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* Author: Aryadev Chavali
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* Commentary: The inplace O(nlog(n)) sortitng algorithm. Originally designed
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* in C, hence the lack of iostream.
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*/
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#include <cstdint>
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#include <cstdio>
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#include <cstdlib>
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#include <fstream>
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#include <iostream>
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#include <stack>
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#include <vector>
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using u64 = uint64_t;
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#define ARR_SIZE(XS) (sizeof(XS) / sizeof((XS)[0]))
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#define SWAP(A, B) \
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do \
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{ \
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(A) ^= (B); \
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(B) ^= (A); \
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(A) ^= (B); \
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} while (0)
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void print_arr(u64 *arr, u64 size)
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{
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printf("{\n");
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for (u64 i = 0; i < size; ++i)
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printf(" %lu,\n", arr[i]);
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printf("}\n");
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}
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struct Partition
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{
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u64 *arr;
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u64 arr_size;
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};
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void quicksort(u64 *arr, u64 arr_size)
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{
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std::stack<Partition> partitions;
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partitions.push({arr, arr_size});
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while (!partitions.empty())
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{
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const auto partition = partitions.top();
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arr = partition.arr;
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arr_size = partition.arr_size;
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partitions.pop();
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// TODO: Use a different sort for small enough sizes?
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if (arr_size > 1)
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{
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// TODO: Choose a better pivot maybe?
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u64 pivot = arr[arr_size - 1]; // Choose the last element as pivot
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u64 pivot_index = -1;
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for (u64 j = 0; j < arr_size; ++j)
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{
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if (arr[j] < pivot)
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{
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++pivot_index;
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std::swap(arr[pivot_index], arr[j]);
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}
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}
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std::swap(arr[pivot_index + 1], arr[arr_size - 1]);
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partitions.push({arr, pivot_index + 1});
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partitions.push({arr + pivot_index + 1, arr_size - pivot_index - 1});
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}
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}
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}
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int main(int argc, char *argv[])
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{
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(void)argc;
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(void)argv;
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#define TEST_SIZE 10
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// randomly generate some numbers
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// u64 *arr = new u64[TEST_SIZE];
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// u64 arr_size = TEST_SIZE;
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// for (size_t i = 0; i < TEST_SIZE; ++i)
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// arr[i] = rand() % (2L << 30);
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// Use nums.txt
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std::ifstream input(argc > 1 ? argv[1] : "nums.txt");
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std::vector<u64> num_vec;
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for (std::string line; std::getline(input, line);
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num_vec.push_back(std::stoi(line)))
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continue;
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u64 *arr = &num_vec[0];
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u64 arr_size = num_vec.size();
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printf("Before: ");
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print_arr(arr, arr_size);
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printf("\n");
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quicksort(arr, arr_size);
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printf("After: ");
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print_arr(arr, arr_size);
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printf("\n");
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// delete[] arr;
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return 0;
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}
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