思路:
static ListNode merge(ListNode l1, ListNode l2) {
ListNode node = null;
while (l1 != null && l2 != null) {
if (l1.value < l2.value) {
if (node == null) {
node = l1;
}else {
node.next = l1;
}
l1 = l1.next;
}else {
if (node == null) {
node = l2;
}else {
node.next = l2;
}
l2 = l2.next;
}
}
while (l1!=null) {
if (node == null) {
node = l1;
}else {
node.next = l1;
}
l1 = l1.next;
}
while (l2!=null) {
if (node == null) {
node = l2;
}else {
node.next = l2;
}
l2 = l2.next;
}
return node;
}