題目十六：合并兩個排序的鏈表
題目描述：
輸入兩個單調(diào)遞增的鏈表，輸出兩個鏈表合成后的鏈表，當然我們需要合成后的鏈表滿足單調(diào)不減規(guī)則。
解題思路：
遞歸版本
public ListNode Merge(ListNode list1,ListNode list2) {
if (list1 == null) {
return list2;
}
if (list2 == null) {
return list1;
}
if(list1.val <= list2.val){
list1.next = Merge(list1.next, list2);
return list1;
}else{
list2.next = Merge(list1, list2.next);
return list2;
}
}
非遞歸版本
public ListNode Merge(ListNode list1,ListNode list2) {
if (list1 == null) {
return list2;
}
if (list2 == null) {
return list1;
}
ListNode mergeHead = null;
ListNode current = null;
while (list1 != null && list2 != null) {
if (list1.val <= list2.val) {
if (mergeHead == null) {
mergeHead = current = list1;
} else {
current.next = list1;
current = current.next;
}
list1 = list1.next;
} else {
if (mergeHead == null) {
mergeHead = current = list2;
} else {
current.next = list2;
current = current.next;
}
list2 = list2.next;
}
}
if (list1 == null) {
current.next = list2;
} else if (list2 == null) {
current.next = list1;
}
return mergeHead;
}
