87 lines
2.6 KiB
C++
87 lines
2.6 KiB
C++
/*******************************************************************************
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*
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* Copyright (c) 2020 Gnarwhal
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*
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* -----------------------------------------------------------------------------
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files(the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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*******************************************************************************/
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#include <vector>
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#include <algorithm>
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#include <string>
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#include <iostream>
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#include <fstream>
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#include "types.hpp"
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// Find 2 numbers that sum to 2020
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auto find_2020_x2(const std::vector<i32> & list) -> void {
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auto begin = 0;
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auto end = list.size() - 1;
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auto sum = 0;
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while ((sum = list[begin] + list[end]) != 2020) {
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if (sum < 2020) {
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++begin;
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} else {
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--end;
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}
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}
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std::cout << (list[begin] * list[end]) << std::endl;
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}
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// Find 3 numbers that sum to 2020
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auto find_2020_x3(const std::vector<i32> & list) -> void {
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for (auto n0 = 0; n0 < list.size() - 2; ++n0) {
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for (auto n1 = 1; n1 < list.size() - 1; ++n1) {
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auto low = n0 + 1;
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auto high = n1;
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auto n2 = (low + high) / 2;
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while (low < high - 1) {
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auto sum = 0;
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if ((sum = list[n0] + list[n1] + list[n2]) == 2020) {
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std::cout << (list[n0] * list[n1] * list[n2]) << std::endl;
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return;
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} else if (sum > 2020) {
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low = n2 + 1;
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} else {
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high = n2;
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}
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}
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}
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}
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}
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auto main(i32 argc, char * argv[]) -> i32 {
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auto list = std::vector<i32>();
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{
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auto line = std::string();
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auto file = std::ifstream("day1.input");
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while (getline(file, line)) {
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list.push_back(std::stoi(line));
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}
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}
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std::sort(list.begin(), list.end());
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find_2020_x2(list);
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find_2020_x3(list);
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return 0;
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}
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