66 lines
2.8 KiB
C++
66 lines
2.8 KiB
C++
/*#############################################################################
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## Author: Shaun Reed ##
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## Legal: All Content (c) 2021 Shaun Reed, all rights reserved ##
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## About: An example implementation of counting sort using a custom library ##
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## + In support of a radix sort implementation ##
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## ##
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## Contact: shaunrd0@gmail.com | URL: www.shaunreed.com | GitHub: shaunrd0 ##
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###############################################################################
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*/
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#include "lib-counting.hpp"
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#include <algorithm>
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#include <vector>
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#include <cstdint>
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void CountingSort(std::vector<int> &array, int placeValue)
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{
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std::vector<int> sortedArray(array.size(), 0);
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// Find the maximum value within the array to sort
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int32_t maxValue = INT32_MIN;
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for (const auto &val : array) maxValue = (val > maxValue) ? val : maxValue;
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// Create an array with element for all *placeValues* within range of the set
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// + Not the size of the array to sort, but instead a element of
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// + tempArray[digit] = 0; Considering only the digit at placeValue of array[n]
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// Using this vector, we have a place to count all possible digits at placeValue
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std::vector<int> tempArray(10, 0);
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// Count the occurrences of each digit at this placeValue within the array
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// + Store the end result as tempArray[digit] = count;
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// + Where digit is found at the decimal placeValue of each value within array
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for (const auto &val : array) {
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// Get the digit at the decimal placeValue of arrayValue
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auto index = static_cast<size_t>((val / placeValue) % tempArray.size());
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// Running total of each value with the same digit at decimal placeValue
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tempArray[index] = tempArray[index] + 1;
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}
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// Count the values less than or equal to each element of tempArray
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// + Since each element stores its own count, just add the count at index i-1
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for (int i = 1; i < tempArray.size(); i++) {
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tempArray[i] = tempArray[i] + tempArray[i - 1];
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}
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for (ssize_t arrayIndex = array.size() - 1; arrayIndex >= 0; arrayIndex--) {
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// Get the value to consider from the unsorted array
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const int &arrayValue = array[arrayIndex];
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// Get the digit at the decimal placeValue of arrayValue
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// + Use this index to update count of values as we use them
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const auto tempIndex =
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static_cast<size_t>((arrayValue / placeValue) % tempArray.size());
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// Store valueCount as a reference so we can update it
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int &valueCount = tempArray[tempIndex];
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// Offset valueCount by 1 to allow for zero index of sortedArray
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sortedArray[valueCount - 1] = arrayValue;
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valueCount = valueCount - 1;
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}
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array = sortedArray;
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}
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