160. 相交链表

题目描述：https://leetcode-cn.com/problems/intersection-of-two-linked-lists

相交链表的定义：2个链表如果相交，则自相交节点开始，后续节点均相交

思路：
1、双指针法
itrA = headA;
itrB = headB;
hasReachedTailForA -> false;
hasReachedTailForB -> false;

while (itrA != nullptr || itrB != nullptr) {
if (itrA == itrB) {
return itrA;
}

if (itrA->next == nullptr && not hasReachedTailForA) {
itrA = headB;
hasReachedTailForA = true;
} else {
itrA = itrA->next;
}

if (itrB->next == nullptr && not hasReachedTailForB) {
itrB = headA;
hasReachedTailForB = true;
} else {
itrB = itrB->next;
}
}

return nullptr;

2、HashTable

while (itrA != nullptr) {
hasTable[itrA] = itrA->val;
itrA = itrA->next;
}

while (itrB != nullptr) {
if (hasTable.find(itrB) != hasTable.end()) {
return itrB;
}

itrB = itrB->next;
}

return nullptr;