#include "s0160_intersection_of_two_linked_lists.hpp"

ListNode *S0160::getIntersectionNode(ListNode *headA, ListNode *headB) {
  // 获取两个链表的长度
  int lenA{0};
  for (ListNode *ptr = headA; ptr != nullptr; ptr = ptr->next) {
    ++lenA;
  }
  int lenB{0};
  for (ListNode *ptr = headB; ptr != nullptr; ptr = ptr->next) {
    ++lenB;
  }
  // 设置两个指针的起始位置
  ListNode *ptrA = headA, *ptrB = headB;
  if (lenA > lenB) {
    for (int i{0}; i < lenA - lenB; ++i) {
      ptrA = ptrA->next;
    }
  } else if (lenA < lenB) {
    for (int i{0}; i < lenB - lenA; ++i) {
      ptrB = ptrB->next;
    }
  }
  // 两个指针开始同时往前
  while (ptrA != nullptr) {
    if (ptrA == ptrB) {
      return ptrA;
    }
    ptrA = ptrA->next;
    ptrB = ptrB->next;
  }
  return nullptr;
}