leetcode 2. 两数相加
给出两个 非空 的链表用来表示两个非负的整数。其中，它们各自的位数是按照 逆序 的方式存储的，并且它们的每个节点只能存储 一位 数字。如果，我们将这两个数相加起来，则会返回一个新的链表来表示它们的和。您可以假设除了数字 0 之外，这两个数都不会以 0 开头。
示例： 输入：(2 -> 4 -> 3) + (5 -> 6 -> 4) 输出：7 -> 0 -> 8 原因：342 + 465 = 807
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
if (l1 == null) {
return l2;
}
if (l2 == null) {
return l1;
}
int jishu = 0;
ListNode res = new ListNode(-1);
ListNode tmp = res;
while (l1 != null && l2 != null) {
int sum = l1.val + l2.val + jishu;
res.next = new ListNode((sum) % 10);
res = res.next;
jishu = (sum) / 10;
l1 = l1.next;
l2 = l2.next;
}
while (l1 != null) {
int sum = l1.val + jishu;
res.next = new ListNode((sum) % 10);
res = res.next;
jishu = (sum) / 10;
l1 = l1.next;
}
while (l2 != null) {
int sum = l2.val + jishu;
res.next = new ListNode((sum) % 10);
res = res.next;
jishu = (sum) / 10;
l2 = l2.next;
}
if (jishu == 1) {
res.next = new ListNode(1);
}
return tmp.next;
}21. 合并两个有序链表
public ListNode mergeTwoLists1(ListNode l1, ListNode l2) {
if (l1 == null) {
return l2;
}
if (l2 == null) {
return l1;
}
ListNode tmp = new ListNode(0);
ListNode res = tmp;
while (l1 != null && l2 != null) {
if (l1.val < l2.val) {
tmp.next = l1;
l1 = l1.next;
} else {
tmp.next = l2;
l2 = l2.next;
}
tmp = tmp.next;
}
while (l1 != null) {
tmp.next = l1;
l1 = l1.next;
tmp = tmp.next;
}
while (l2 != null) {
tmp.next = l2;
l2 = l2.next;
tmp = tmp.next;
}
return res.next;
}
//递归写法
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if (l1 == null) {
return l2;
}
if (l2 == null) {
return l1;
}
if(l1.val<l2.val){
l1.next = mergeTwoLists(l1.next,l2);
return l1;
}else {
l2.next = mergeTwoLists(l1,l2.next);
return l2;
}
}leetcode 82. 删除排序链表中的重复元素 II
//递归写法
public ListNode deleteDuplicates(ListNode head) {
if (head == null) {
return head;
}
if (head.next != null && head.val == head.next.val) {
while (head != null && head.next != null && head.val == head.next.val) {
head = head.next;
}
//去掉所有重复的数字，然后进行递归
return deleteDuplicates(head.next);
} else {
head.next = deleteDuplicates(head.next);
}
return head;
}
//非递归写法
public ListNode deleteDuplicates1(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode res = new ListNode(-1);
ListNode node = res;
while (head != null) {
boolean dup = false;
while (head != null && head.next != null && head.val == head.next.val) {
head = head.next;
dup = true;
}
if (!dup) {
res.next = head;
res = res.next;
}
head = head.next;
}
res.next = null; //防止res后面还有重复的节点
return node.next;
}83. 删除排序链表中的重复元素
给定一个排序链表，删除所有重复的元素，使得每个元素只出现一次。
示例 1: 输入: 1->1->2 输出: 1->2
示例 2: 输入: 1->1->2->3->3 输出: 1->2->3
public ListNode deleteDuplicates1(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode res = head;
while (head != null && head.next != null) {
//相等的话就删除下一个节点
if (head.val == head.next.val) {
head.next = head.next.next;
} else {
//不相等的话向前移动一位
head = head.next;
}
}
return res;
}
//递归写法
public ListNode deleteDuplicates(ListNode head) {
if (head == null || head.next == null) {
return head;
}
if (head.val == head.next.val) {
//如果值和下一个值相同，删掉这个节点，即直接返回下一个节点
return deleteDuplicates(head.next);
} else {
head.next = deleteDuplicates(head.next);
}
return head;
}
leetcode 86. 分隔链表
public ListNode partition(ListNode head, int x) {
if(head == null || head.next == null){
return head;
}
ListNode more = new ListNode(-1);
ListNode moreHead = more;
ListNode less = new ListNode(-1);
ListNode lessHead = less;
while (head != null){
if(head.val < x){
less.next = head;
less = less.next;
}else {
more.next = head;
more = more.next;
}
head = head.next;
}
more.next = null; //这步不要忘记，不然链表就出现环了
less.next = moreHead.next;
return lessHead.next;
}
