75 lines
2 KiB
C++
75 lines
2 KiB
C++
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#pragma once
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#include <algorithm>
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#include <nall/utility.hpp>
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//class: merge sort
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//average: O(n log n)
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//worst: O(n log n)
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//memory: O(n)
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//stack: O(log n)
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//stable?: yes
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//note: merge sort was chosen over quick sort, because:
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//* it is a stable sort
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//* it lacks O(n^2) worst-case overhead
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#define NALL_SORT_INSERTION
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//#define NALL_SORT_SELECTION
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namespace nall {
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template<typename T, typename Comparator> auto sort(T list[], unsigned size, const Comparator& lessthan) -> void {
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if(size <= 1) return; //nothing to sort
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//use insertion sort to quickly sort smaller blocks
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if(size < 64) {
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#if defined(NALL_SORT_INSERTION)
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for(signed i = 1, j; i < size; i++) {
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T copy = std::move(list[i]);
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for(j = i - 1; j >= 0; j--) {
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if(!lessthan(copy, list[j])) break;
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list[j + 1] = std::move(list[j]);
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}
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list[j + 1] = std::move(copy);
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}
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#elif defined(NALL_SORT_SELECTION)
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for(unsigned i = 0; i < size; i++) {
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unsigned min = i;
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for(unsigned j = i + 1; j < size; j++) {
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if(lessthan(list[j], list[min])) min = j;
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}
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if(min != i) std::swap(list[i], list[min]);
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}
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#endif
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return;
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}
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//split list in half and recursively sort both
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unsigned middle = size / 2;
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sort(list, middle, lessthan);
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sort(list + middle, size - middle, lessthan);
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//left and right are sorted here; perform merge sort
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T* buffer = new T[size];
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unsigned offset = 0, left = 0, right = middle;
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while(left < middle && right < size) {
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if(!lessthan(list[right], list[left])) {
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buffer[offset++] = std::move(list[left++]);
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} else {
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buffer[offset++] = std::move(list[right++]);
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}
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}
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while(left < middle) buffer[offset++] = std::move(list[left++]);
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while(right < size) buffer[offset++] = std::move(list[right++]);
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for(unsigned i = 0; i < size; i++) list[i] = std::move(buffer[i]);
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delete[] buffer;
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}
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template<typename T> auto sort(T list[], unsigned size) -> void {
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return sort(list, size, [](const T& l, const T& r) { return l < r; });
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}
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}
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