mirror of https://github.com/bsnes-emu/bsnes.git
63 lines
1.6 KiB
C++
Executable File
63 lines
1.6 KiB
C++
Executable File
#ifndef NALL_SORT_HPP
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#define NALL_SORT_HPP
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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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//notes:
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//there are two primary reasons for choosing merge sort
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//over the (usually) faster quick sort*:
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//1: it is a stable sort.
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//2: it lacks O(n^2) worst-case overhead.
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//(* which is also O(n log n) in the average case.)
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namespace nall {
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template<typename T>
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void sort(T list[], unsigned length) {
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if(length <= 1) return; //nothing to sort
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//use insertion sort to quickly sort smaller blocks
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if(length < 64) {
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for(unsigned i = 0; i < length; i++) {
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unsigned min = i;
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for(unsigned j = i + 1; j < length; j++) {
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if(list[j] < list[min]) min = j;
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}
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if(min != i) swap(list[i], list[min]);
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}
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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 = length / 2;
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sort(list, middle);
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sort(list + middle, length - middle);
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//left and right are sorted here; perform merge sort
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T *buffer = new T[length];
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unsigned offset = 0;
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unsigned left = 0;
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unsigned right = middle;
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while(left < middle && right < length) {
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if(list[left] < list[right]) {
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buffer[offset++] = list[left++];
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} else {
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buffer[offset++] = list[right++];
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}
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}
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while(left < middle) buffer[offset++] = list[left++];
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while(right < length) buffer[offset++] = list[right++];
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for(unsigned i = 0; i < length; i++) list[i] = buffer[i];
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delete[] buffer;
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}
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}
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#endif
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