comments	difficulty	edit_url	tags
true	中等	https://github.com/doocs/leetcode/edit/main/solution/0300-0399/0369.Plus%20One%20Linked%20List/README.md	链表 数学

369. 给单链表加一 🔒

English Version

题目描述

给定一个用链表表示的非负整数， 然后将这个整数 再加上 1 。

这些数字的存储是这样的：最高位有效的数字位于链表的首位 head 。

 

示例 1:

输入: head = [1,2,3]
输出: [1,2,4]

示例 2:

输入: head = [0]
输出: [1]

 

提示：

• 链表中的节点数在 [1, 100] 的范围内。
• 0 <= Node.val <= 9
• 由链表表示的数字不包含前导零，除了零本身。

解法

方法一：链表遍历

我们先设置一个虚拟头节点 $\textit{dummy}$，初始时 $\textit{dummy}$ 的值为 $0$，并且 $\textit{dummy}$ 的后继节点为链表 $\textit{head}$。

接下来，我们从虚拟头节点开始遍历链表，找到最后一个不为 $9$ 的节点，将其值加 $1$，并将该节点之后的所有节点的值置为 $0$。

最后，我们判断虚拟头节点的值是否为 $1$，如果为 $1$，则返回 $\textit{dummy}$，否则返回 $\textit{dummy}$ 的后继节点。

时间复杂度 $O(n)$，其中 $n$ 是链表的长度。空间复杂度 $O(1)$。

Python3

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def plusOne(self, head: Optional[ListNode]) -> Optional[ListNode]:
        dummy = ListNode(0, head)
        target = dummy
        while head:
            if head.val != 9:
                target = head
            head = head.next
        target.val += 1
        target = target.next
        while target:
            target.val = 0
            target = target.next
        return dummy if dummy.val else dummy.next

Java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode plusOne(ListNode head) {
        ListNode dummy = new ListNode(0, head);
        ListNode target = dummy;
        while (head != null) {
            if (head.val != 9) {
                target = head;
            }
            head = head.next;
        }
        ++target.val;
        target = target.next;
        while (target != null) {
            target.val = 0;
            target = target.next;
        }
        return dummy.val == 1 ? dummy : dummy.next;
    }
}

C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* plusOne(ListNode* head) {
        ListNode* dummy = new ListNode(0, head);
        ListNode* target = dummy;
        for (; head; head = head->next) {
            if (head->val != 9) {
                target = head;
            }
        }
        target->val++;
        for (target = target->next; target; target = target->next) {
            target->val = 0;
        }
        return dummy->val ? dummy : dummy->next;
    }
};

Go

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func plusOne(head *ListNode) *ListNode {
	dummy := &ListNode{0, head}
	target := dummy
	for head != nil {
		if head.Val != 9 {
			target = head
		}
		head = head.Next
	}
	target.Val++
	for target = target.Next; target != nil; target = target.Next {
		target.Val = 0
	}
	if dummy.Val == 1 {
		return dummy
	}
	return dummy.Next
}

TypeScript

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     val: number
 *     next: ListNode | null
 *     constructor(val?: number, next?: ListNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.next = (next===undefined ? null : next)
 *     }
 * }
 */

function plusOne(head: ListNode | null): ListNode | null {
    const dummy = new ListNode(0, head);
    let target = dummy;
    while (head) {
        if (head.val !== 9) {
            target = head;
        }
        head = head.next;
    }
    target.val++;
    for (target = target.next; target; target = target.next) {
        target.val = 0;
    }
    return dummy.val ? dummy : dummy.next;
}