Aryadev Chavali
ab5d1c6997
This generates a new list, and appends to it every time the current list value satisfies the condition. It then recursively calls the filter on the next value.
111 lines
2.1 KiB
C++
111 lines
2.1 KiB
C++
/* list.cpp
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* Date: 2021-11-20
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* Author: Aryadev Chavali
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*/
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#include <cstdio>
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#include <iostream>
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#include <cstdlib>
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template <typename T>
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struct List
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{
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T value;
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struct List<T> *next;
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~List()
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{
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if (next == nullptr)
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return;
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delete next;
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}
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};
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template <typename T>
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List<T> *append(List<T> *lst, T value)
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{
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List<T> *node;
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if (lst == nullptr)
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{
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node = new List<T>;
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node->value = value;
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node->next = nullptr;
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return node;
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}
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for (node = lst; node->next != nullptr; node = node->next)
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continue;
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node->next = new List<T>;
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node->next->value = value;
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node->next->next = nullptr;
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return lst;
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}
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/** Reverse a list
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*/
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template <typename T>
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List<T> *reverse(List<T> *lst, List<T> *prev = nullptr)
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{
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auto next = lst->next;
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lst->next = prev;
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if (next == nullptr)
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return lst;
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return reverse(next, lst);
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}
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template <typename T, typename U>
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void map(List<T> *lst, U (*f)(T))
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{
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if (!lst)
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return;
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lst->value = f(lst->value);
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map(lst->next, f);
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}
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template <typename T>
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T reduce(List<T> *lst, T (*reducer) (T, T), T init = 0)
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{
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if (!lst)
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return init;
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if (!init)
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init = lst->value;
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else
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init = reducer(init, lst->value);
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return reduce(lst->next, reducer, init);
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}
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template <typename T>
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List<T> *filter(List<T> *lst, bool (*f)(T), List<T> *new_lst = nullptr)
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{
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if (!lst)
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return new_lst;
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if (f(lst->value))
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new_lst = append(new_lst, lst->value);
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return filter(lst->next, f, new_lst);
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}
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template <typename T>
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std::ostream& operator<<(std::ostream& ostream, const List<T> *lst)
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{
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if (!lst)
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return ostream;
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ostream << "|" << lst->value << lst->next;
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return ostream;
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}
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int main(void)
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{
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auto lst = append<int>(nullptr, 1);
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for (int i = 2; i < 10; ++i)
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lst = append(lst, i);
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std::cout << lst << std::endl;
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lst = reverse(lst);
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std::cout << lst << std::endl;
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map<int, int>(lst = reverse(lst), [](int x){ return x * 2; });
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std::cout << lst << std::endl;
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std::cout << reduce<int>(lst, [](int a, int b) { return a + b; }, 0) << std::endl;
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delete lst;
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return 0;
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}
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