62 lines
2.9 KiB
C++
62 lines
2.9 KiB
C++
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// fig12_09.cpp
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// binarySearch function with a precondition requiring a sorted vector.
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#include <algorithm>
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#include <iostream>
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#include <vector>
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template<class T>
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int binarySearch(const std::vector<T>& items, const T& key)
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[[pre: items.size() > 0]]
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[[pre audit: std::is_sorted(items.begin(), items.end())]] {
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size_t low{0}; // low index of elements to search
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size_t high{items.size() - 1}; // high index
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size_t middle{(low + high + 1) / 2}; // middle element
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int loc{-1}; // key's index; -1 if not found
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do { // loop to search for element
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// if the element is found at the middle
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if (key == items[middle]) {
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loc = middle; // loc is the current middle
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}
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else if (key < items[middle]) { // middle is too high
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high = middle - 1; // eliminate the higher half
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}
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else { // middle element is too low
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low = middle + 1; // eliminate the lower half
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}
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middle = (low + high + 1) / 2; // recalculate the middle
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} while ((low <= high) && (loc == -1));
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return loc; // return location of key
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}
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int main() {
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// sorted vector v1 satisfies binarySearch's sorted vector precondition
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std::vector v1{10, 20, 30, 40, 50, 60, 70, 80, 90};
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int result1{binarySearch(v1, 70)};
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std::cout << "70 was " << (result1 != -1 ? "" : "not ") << "found in v1\n";
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// unsorted vector v2 violates binarySearch's sorted vector precondition
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std::vector v2{60, 70, 80, 90, 10, 20, 30, 40, 50};
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int result2{binarySearch(v2, 60)};
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std::cout << "60 was " << (result2 != -1 ? "" : "not ") << "found in v2\n";
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}
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/**************************************************************************
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* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The authors *
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* and publisher shall not be liable in any event for incidental or *
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* consequential damages in connection with, or arising out of, the *
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* furnishing, performance, or use of these programs. *
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**************************************************************************/
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