67 lines
2.3 KiB
C++
67 lines
2.3 KiB
C++
#include <algorithm>
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#include <iostream>
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#include <vector>
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std::vector<std::size_t> getReversalsToSort(const std::vector<int> &arr);
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/**
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* Imagine a sort algorithm, that sorts array of integers by repeatedly
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* reversing the order of the first several elements of it.
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*
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* For example, to sort [12,13,11,14], you need to reverse the order of the
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* first two (2) elements. You will get [13,12,11,14]. Then you shall reverse
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* the order of the first three (3) elements, and you will get [11,12,13,14]
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*
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* For this assignment you shall implement function
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* that returns list of integers corresponding to the required reversals.
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* E.g. for given vector [12,13,11,14]
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* the function should return [2, 3].
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*/
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std::vector<std::size_t> getReversalsToSort(const std::vector<int> &arr) {
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// there's a slightly more fancy version of this but who cares
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// all we need is the elements sorted from least to greatest
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// sorting to get info might be cheating but eeeeeh it wasn't specified
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std::vector<int> sorted = arr;
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std::sort(sorted.begin(), sorted.end());
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std::vector<std::size_t> ret = {};
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// a bit more explicit than necessary but my brain thought it was useful info
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std::vector<int>::const_iterator search_reference = arr.cbegin();
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std::size_t i = arr.size();
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for (auto elem = sorted.rbegin(); elem != sorted.rend(); elem++) {
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// using search reference so we don't find the same element over and over
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// again
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search_reference = std::find(search_reference, arr.cend(), *elem);
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std::size_t first_swap = search_reference - arr.cbegin() + 1;
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std::size_t second_swap = i;
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// remove false positives of elements already being in the correct spot
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// also remove cases where nothing changes in one of the reverses
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// (that should never happen)
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if (first_swap != second_swap && first_swap > 1 && second_swap > 1) {
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ret.push_back(first_swap);
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ret.push_back(second_swap);
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}
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i--;
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// pushing the search reference past what we just found so we don't find
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// it again
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if ((elem + 1) != sorted.rend() && *(elem + 1) == *elem) {
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search_reference++;
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} else {
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search_reference = arr.cbegin();
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}
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}
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return ret;
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}
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int main(void) {
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std::cout << "{";
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std::vector<int> arr{12, 13, 11, 14};
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for (auto &e : getReversalsToSort(arr)) {
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std::cout << e << ",";
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}
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std::cout << "}\n";
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}
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