#include "Solution142.hpp"

Solution142::ListNode * Solution142::detectCycle(ListNode *head) {

if (!head) {

return nullptr;

}

auto slow_ptr = head;

auto fast_ptr = head;

while (fast_ptr && fast_ptr->next) {

slow_ptr = slow_ptr->next;

fast_ptr = fast_ptr->next->next;

if (fast_ptr == slow_ptr) {

auto ano_ptr = head;

while (ano_ptr != slow_ptr) {

ano_ptr = ano_ptr->next;

slow_ptr = slow_ptr->next;

}

return ano_ptr;

}

}

return nullptr;

}