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96 lines
2.3 KiB
Markdown
96 lines
2.3 KiB
Markdown
# [445. Add Two Numbers II](https://leetcode.com/problems/add-two-numbers-ii/)
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## 题目
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You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
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You may assume the two numbers do not contain any leading zero, except the number 0 itself.
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**Follow up**:
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What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
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**Example**:
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```
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Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
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Output: 7 -> 8 -> 0 -> 7
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```
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## 题目大意
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这道题是第 2 题的变种题，第 2 题中的 2 个数是从个位逆序排到高位，这样相加只用从头交到尾，进位一直进位即可。这道题目中强制要求不能把链表逆序。2 个数字是从高位排到低位的，这样进位是倒着来的。
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## 解题思路
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思路也不难，加法只用把短的链表依次加到长的链表上面来就可以了，最终判断一下最高位有没有进位，有进位再往前进一位。加法的过程可以用到递归。
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## 代码
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```go
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package leetcode
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/**
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* Definition for singly-linked list.
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* type ListNode struct {
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* Val int
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* Next *ListNode
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* }
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*/
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func addTwoNumbers445(l1 *ListNode, l2 *ListNode) *ListNode {
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if l1 == nil {
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return l2
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}
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if l2 == nil {
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return l1
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}
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l1Length := getLength(l1)
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l2Length := getLength(l2)
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newHeader := &ListNode{Val: 1, Next: nil}
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if l1Length < l2Length {
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newHeader.Next = addNode(l2, l1, l2Length-l1Length)
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} else {
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newHeader.Next = addNode(l1, l2, l1Length-l2Length)
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}
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if newHeader.Next.Val > 9 {
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newHeader.Next.Val = newHeader.Next.Val % 10
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return newHeader
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}
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return newHeader.Next
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}
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func addNode(l1 *ListNode, l2 *ListNode, offset int) *ListNode {
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if l1 == nil {
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return nil
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}
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var (
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res, node *ListNode
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)
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if offset == 0 {
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res = &ListNode{Val: l1.Val + l2.Val, Next: nil}
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node = addNode(l1.Next, l2.Next, 0)
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} else {
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res = &ListNode{Val: l1.Val, Next: nil}
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node = addNode(l1.Next, l2, offset-1)
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}
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if node != nil && node.Val > 9 {
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res.Val++
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node.Val = node.Val % 10
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}
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res.Next = node
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return res
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}
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func getLength(l *ListNode) int {
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count := 0
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cur := l
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for cur != nil {
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count++
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cur = cur.Next
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}
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return count
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}
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``` |