90 lines
2.2 KiB
C++
90 lines
2.2 KiB
C++
/*
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VIM: let b:cf5build="clang -std=c++20 -O2 -pthread -lstdc++ -I. {SRC} -o {OUT}"
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VIM: let b:cf5run="{OUT}"
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*/
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#include <iostream>
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#include <exception>
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#include <chrono>
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#include <string>
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#include <vector>
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#include <unordered_map>
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#include <unordered_set>
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#include <functional>
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/*
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https://app.codility.com/programmers/lessons/99-future_training/array_inversion_count/
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An array A consisting of N integers is given. An inversion is a pair of indexes (P, Q) such that P < Q and A[Q] < A[P].
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Write a function:
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int solution(vector<int> &A);
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that computes the number of inversions in A, or returns −1 if it exceeds 1,000,000,000.
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For example, in the following array:
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A[0] = -1 A[1] = 6 A[2] = 3
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A[3] = 4 A[4] = 7 A[5] = 4
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there are four inversions:
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(1,2) (1,3) (1,5) (4,5)
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so the function should return 4.
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Write an efficient algorithm for the following assumptions:
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N is an integer within the range [0..100,000];
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each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
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*/
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int solution(const std::vector<int>& v)
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{
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std::vector<size_t> iv(v.size(),0);
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for (size_t i=0; i<v.size(); ++i){
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iv[i] = i;
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}
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std::stable_sort(iv.begin(), iv.end(), [&v](size_t op1, size_t op2){
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return v[op1] < v[op2];
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});
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size_t count = 0;
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for (size_t i=0; i < iv.size(); ++i){
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if ( i < iv[i]){
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count += iv[i] - i;
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}
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}
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return count;
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}
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int main ( void )
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{try{
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auto begin = std::chrono::high_resolution_clock::now();
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std::cout << solution({-1, 6, 3, 4, 7, 4}) << std::endl;
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std::cout << solution({0, 0, 0, 1, 1, 1}) << std::endl;
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std::cout << solution({0, 1, 0, 1, 1, 1}) << std::endl;
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std::cout << solution({0}) << std::endl;
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std::cout << solution({}) << std::endl;
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auto end = std::chrono::high_resolution_clock::now();
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std::chrono::duration<double> seconds = end - begin;
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std::cout << "Time: " << seconds.count() << std::endl;
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return 0;
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}
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catch ( const std::exception& e )
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{
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std::cerr << std::endl
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<< "std::exception(\"" << e.what() << "\")." << std::endl;
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return 2;
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}
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catch ( ... )
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{
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std::cerr << std::endl
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<< "unknown exception." << std::endl;
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return 1;
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}}
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