一起刷算法与数据结构-链表篇2

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
      auto dummy = new ListNode(-1);
      dummy->next=head;
      auto per = dummy,cur = dummy->next;
      while(cur && cur->next)
      {
          auto temp = cur->next;
          per->next = temp;
          cur->next = temp->next;
          temp->next = cur;
          per=cur;
          cur=cur->next;
      }
      return dummy->next;

    }
};

class Solution {
public:
    vector<int> nextLargerNodes(ListNode* head) {
           vector<int>l;
           vector<int>ans;
           for(auto p=head;p;p=p->next)
           {
               l.push_back(p->val);
           }
           stack<int>s;
           for(int i=l.size()-1;i>=0;i--)
           {
               if(!s.empty() && l[i]<s.top())
               {
                   ans.push_back(s.top());
               }
               else
               {
                   
                   while(!s.empty() && l[i]>=s.top())
                   {
                       s.pop();    
                   }
                   if(!s.empty()) ans.push_back(s.top());
                   else ans.push_back(0);
               }

                s.push(l[i]);
                
           }
           //return ans;
           for(int i=0;i<ans.size()/2;i++)
           {
               swap(ans[i],ans[ans.size()-i-1]);
           }
           return ans;
    }
};