Two Sum
Brute Force: time O(n^2) space O(1)
Hash Map: time O(n) space O(n)
Add Two Numbers
Unconsidered:
[1]+[9,9]-> after l1 ends and l2 ends, there is still one carry
Struct initiation in C++: new ListNode(0)
if (temp->val==0) temp==0
change to
if (temp->val==0) {
l4 = l3;
while(l4->next!=NULL){
if(l4 ->next==temp) l4->next = NULL;
else l4=l4->next;
}
}
first one simply let temp points to NULL, but doesn't change the front node's next pointer, so l4 is needed as the front node then set its next to NULL.