將兩個(gè)有序鏈表合并為一個(gè)新的有序鏈表并返回乔夯。
新鏈表是通過(guò)拼接給定的兩個(gè)鏈表的所有節(jié)點(diǎn)組成的。
示例：
輸入：1->2->4, 1->3->4
輸出：1->1->2->3->4->4
解法一：
迭代求解。
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
//一定要先實(shí)例化一個(gè)結(jié)點(diǎn)
ListNode head = new ListNode(0);
//定義一個(gè)結(jié)點(diǎn)變量指向頭結(jié)點(diǎn)
ListNode l3 = head;
while (l1 != null && l2 != null) {
if (l1.val <= l2.val) {
head.next = l1;
l1 = l1.next;
head = head.next;
} else {
head.next = l2;
l2 = l2.next;
head = head.next;
}
}
while (l1 != null) {
head.next = l1;
l1 = l1.next;
head = head.next;
}
while (l2 != null) {
head.next = l2;
l2 = l2.next;
head = head.next;
}
return l3.next;
}
解法二：
遞歸求解育拨。
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if (l1 == null) return l2;
if (l2 == null) return l1;
ListNode head = null;
if (l1.val <= l2.val) {
head = l1;
head.next = mergeTwoLists(l1.next, l2);
} else {
head = l2;
head.next = mergeTwoLists(l2.next, l1);
}
return head;
}
