Leetcode:21. Merge Two Sorted Lists(JAVA)

【问题描述】

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first
two lists.

【思路】

维护两个指针，依次遍历l1, l2

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if (l1 == null) {
return l2;
}

if (l2 == null) {
return l1;
}
ListNode head = null, end = null, t1 = l1, t2 = l2;
while (t1 != null && t2 != null) {
if (t1.val <= t2.val) {
if (head == null) {
head = t1;
end = head;
}else {
end.next = t1;
end = end.next;
}
t1 = t1.next;
}else {
if (head == null) {
head = t2;
end = head;
}else {
end.next = t2;
end = end.next;
}
t2 = t2.next;
}
}

if (t1 == null) {
end.next = t2;
}else {
end.next = t1;
}
return head;
}