添加两数相加解法

Author: hongqima

0002-两数相加/Swift/addTwoNumbers.swift

@@ -0,0 +1,59 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public var val: Int
+ *     public var next: ListNode?
+ *     public init(_ val: Int) {
+ *         self.val = val
+ *         self.next = nil
+ *     }
+ * }
+ */
+
+/**
+ 执行用时 : 72 ms, 在Add Two Numbers的Swift提交中击败了93.53% 的用户
+ 内存消耗 : 21.5 MB, 在Add Two Numbers的Swift提交中击败了5.14% 的用户
+ 
+ 1. 使用flag标识当前是否需要进位
+ 2. 共同遍历两个链表，取两个结点和flag的和，并重设flag
+ 3. 处理比较长的链表
+ 4. 最终处理flag
+ */
+func addTwoNumbers(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
+  var flag = 0
+  var p = l1
+  var q = l2
+  var dummy = ListNode(-1)
+  var rear = dummy
+  while p != nil && q != nil {
+    let val = p!.val + q!.val + flag
+    let newNode = ListNode(val % 10)
+    flag = val / 10
+    rear.next = newNode
+    rear = newNode
+    p = p!.next
+    q = q!.next
+  }
+  while p != nil {
+    print(p!.val)
+    let val = p!.val + flag
+    let newNode = ListNode(val % 10)
+    flag = val / 10
+    rear.next = newNode
+    rear = newNode
+    p = p!.next
+  }
+  
+  while q != nil {
+    let val = q!.val + flag
+    let newNode = ListNode(val % 10)
+    flag = val / 10
+    rear.next = newNode
+    rear = newNode
+    q = q!.next
+  }
+  if flag != 0 {
+    rear.next = ListNode(1)
+  }
+  return dummy.next
+}

README.md

@@ -11,7 +11,7 @@
 | 题号 | 题目 | 难度 | Swift | Python | Java | C/C++ | OC |
 | --- | ---- | --- | ----- | ------ | ---- | ----- | -- |
 | 1 | [两数之和](https://leetcode-cn.com/problems/two-sum) | 简单 | [Swift](0001-两数之和/Swift) |  |  |  |  |
-| 2 | [两数相加](https://leetcode-cn.com/problems/add-two-numbers) | 中等 | | | | | |
+| 2 | [两数相加](https://leetcode-cn.com/problems/add-two-numbers) | 中等 | [Swift](0002-两数相加/Swift) | | | | |
 | 3 | [无重复字符的最长子串](https://leetcode-cn.com/problems/longest-substring-without-repeating-characters) | 中等 | | | | | |
 | 4 | [寻找两个有序数组的中位数](https://leetcode-cn.com/problems/median-of-two-sorted-arrays) | 困难 | | | | | |
 | 5 | [最长回文子串](https://leetcode-cn.com/problems/longest-palindromic-substring) | 中等 | | | | | |