摘要：
class Solution {public: int numTrees(int n) { vector v(n+1, 0); v[0] = 1; v[1] = 1; v[2] = 2; if(n<=2) return v[n]; for(int i=3; i<=n; i++) for(int j=1; j<=i; j++) v[i] += v[j-1]*v[i-j]; return v[n]; ... 阅读全文
摘要：
class Solution {public: ListNode *swapPairs(ListNode *head) { if(head==NULL)return NULL; ListNode *p=head,*ppre=head,*pnext; while(p&&p->next) { pnext=p->next; if(pnext) { if(ppre==head)head=pnext; else... 阅读全文