369. Plus One Linked List

Description

Given a non-negative integer represented as a linked list of digits, plus one to the integer.

The digits are stored such that the most significant digit is at the head of the list.

 

Example 1:

Input: head = [1,2,3]
Output: [1,2,4]

Example 2:

Input: head = [0]
Output: [1]

 

Constraints:

  • The number of nodes in the linked list is in the range [1, 100].
  • 0 <= Node.val <= 9
  • The number represented by the linked list does not contain leading zeros except for the zero itself. 

Solutions

Solution 1

Python Code
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# 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: ListNode) -> 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 Code
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/**
 * 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++ Code
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/**
 * 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;
        while (head) {
            if (head->val != 9) target = head;
            head = head->next;
        }
        ++target->val;
        target = target->next;
        while (target) {
            target->val = 0;
            target = target->next;
        }
        return dummy->val == 1 ? dummy : dummy->next;
    }
};

Go Code
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/**
 * 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++
	target = target.Next
	for target != nil {
		target.Val = 0
		target = target.Next
	}
	if dummy.Val == 1 {
		return dummy
	}
	return dummy.Next
}