38 lines
1.0 KiB
C++
38 lines
1.0 KiB
C++
#include <iterator>
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#include <algorithm>
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#include <functional>
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#include <cstdlib>
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#include <ctime>
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#include <iostream>
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template <typename Iterator>
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Iterator select(Iterator begin, Iterator end, int n) {
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typedef typename std::iterator_traits<Iterator>::value_type T;
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while (true) {
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Iterator pivotIt = begin + std::rand() % std::distance(begin, end);
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std::iter_swap(pivotIt, end-1); // Move pivot to end
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pivotIt = std::partition(begin, end-1, std::bind2nd(std::less<T>(), *(end-1)));
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std::iter_swap(end-1, pivotIt); // Move pivot to its final place
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if (n == pivotIt - begin) {
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return pivotIt;
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} else if (n < pivotIt - begin) {
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end = pivotIt;
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} else {
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n -= pivotIt+1 - begin;
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begin = pivotIt+1;
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}
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}
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}
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int main() {
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std::srand(std::time(NULL));
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for (int i = 0; i < 10; i++) {
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int a[] = {9, 8, 7, 6, 5, 0, 1, 2, 3, 4};
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std::cout << *select(a, a + sizeof(a)/sizeof(*a), i);
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if (i < 9) std::cout << ", ";
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}
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std::cout << std::endl;
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return 0;
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}
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