unordered_map
链表中环的入口结点
http://www.nowcoder.com/questionTerminal/253d2c59ec3e4bc68da16833f79a38e4
class Solution {
public:
ListNode* EntryNodeOfLoop(ListNode* pHead)
{
unordered_map<ListNode*, bool> nodemap;
while(pHead){
if(nodemap.find(pHead) != nodemap.end()) return pHead;
else{
nodemap[pHead] = true;
}
pHead = pHead->next;
}
return nullptr;
}
}; 