From 7b236b56b620c8bc218b6c23d7d8550408f05ae4 Mon Sep 17 00:00:00 2001
From: YDZ <ydz627@gmail.com>
Date: Tue, 19 Feb 2019 13:42:09 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20problem=202?=
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---
 .../2.Add-Two-Number/Add Two Numbers.go       |  43 +++++++
 .../2.Add-Two-Number/Add Two Numbers_test.go  | 111 ++++++++++++++++++
 Algorithms/2.Add-Two-Number/README.md         |  30 +++++
 3 files changed, 184 insertions(+)
 create mode 100644 Algorithms/2.Add-Two-Number/Add Two Numbers.go
 create mode 100644 Algorithms/2.Add-Two-Number/Add Two Numbers_test.go
 create mode 100644 Algorithms/2.Add-Two-Number/README.md

diff --git a/Algorithms/2.Add-Two-Number/Add Two Numbers.go b/Algorithms/2.Add-Two-Number/Add Two Numbers.go
new file mode 100644
index 00000000..0b85531e
--- /dev/null
+++ b/Algorithms/2.Add-Two-Number/Add Two Numbers.go	
@@ -0,0 +1,43 @@
+package leetcode
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
+	if l1 == nil || l2 == nil {
+		return nil
+	}
+	head := &ListNode{Val: 0, Next: nil}
+	current := head
+	carry := 0
+	for l1 != nil || l2 != nil {
+		var x, y int
+		if l1 == nil {
+			x = 0
+		} else {
+			x = l1.Val
+		}
+		if l2 == nil {
+			y = 0
+		} else {
+			y = l2.Val
+		}
+		current.Next = &ListNode{Val: (x + y + carry) % 10, Next: nil}
+		current = current.Next
+		carry = (x + y + carry) / 10
+		if l1 != nil {
+			l1 = l1.Next
+		}
+		if l2 != nil {
+			l2 = l2.Next
+		}
+	}
+	if carry > 0 {
+		current.Next = &ListNode{Val: carry % 10, Next: nil}
+	}
+	return head.Next
+}
diff --git a/Algorithms/2.Add-Two-Number/Add Two Numbers_test.go b/Algorithms/2.Add-Two-Number/Add Two Numbers_test.go
new file mode 100644
index 00000000..24d9d9fd
--- /dev/null
+++ b/Algorithms/2.Add-Two-Number/Add Two Numbers_test.go	
@@ -0,0 +1,111 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question2 struct {
+	para2
+	ans2
+}
+
+// para 是参数
+// one 代表第一个参数
+type para2 struct {
+	one     []int
+	another []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans2 struct {
+	one []int
+}
+
+func Test_Problem2(t *testing.T) {
+
+	qs := []question2{
+
+		question2{
+			para2{[]int{}, []int{}},
+			ans2{[]int{}},
+		},
+
+		question2{
+			para2{[]int{1}, []int{1}},
+			ans2{[]int{2}},
+		},
+
+		question2{
+			para2{[]int{1, 2, 3, 4}, []int{1, 2, 3, 4}},
+			ans2{[]int{2, 4, 6, 8}},
+		},
+
+		question2{
+			para2{[]int{1, 2, 3, 4, 5}, []int{1, 2, 3, 4, 5}},
+			ans2{[]int{2, 4, 6, 8, 0, 1}},
+		},
+
+		question2{
+			para2{[]int{1}, []int{9, 9, 9, 9, 9}},
+			ans2{[]int{0, 0, 0, 0, 0, 1}},
+		},
+
+		question2{
+			para2{[]int{9, 9, 9, 9, 9}, []int{1}},
+			ans2{[]int{0, 0, 0, 0, 0, 1}},
+		},
+
+		question2{
+			para2{[]int{2, 4, 3}, []int{5, 6, 4}},
+			ans2{[]int{7, 0, 8}},
+		},
+
+		question2{
+			para2{[]int{1, 8, 3}, []int{7, 1}},
+			ans2{[]int{8, 9, 3}},
+		},
+		// 如需多个测试，可以复制上方元素。
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 2------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans2, q.para2
+		fmt.Printf("【input】:%v       【output】:%v\n", p, L2s(addTwoNumbers(S2l(p.one), S2l(p.another))))
+	}
+	fmt.Printf("\n\n\n")
+}
+
+// // convert *ListNode to []int
+// func L2s(head *ListNode) []int {
+// 	res := []int{}
+
+// 	for head != nil {
+// 		res = append(res, head.Val)
+// 		head = head.Next
+// 	}
+
+// 	return res
+// }
+
+// // convert []int to *ListNode
+// func S2l(nums []int) *ListNode {
+// 	if len(nums) == 0 {
+// 		return nil
+// 	}
+
+// 	res := &ListNode{
+// 		Val: nums[0],
+// 	}
+// 	temp := res
+// 	for i := 1; i < len(nums); i++ {
+// 		temp.Next = &ListNode{
+// 			Val: nums[i],
+// 		}
+// 		temp = temp.Next
+// 	}
+
+// 	return res
+// }
diff --git a/Algorithms/2.Add-Two-Number/README.md b/Algorithms/2.Add-Two-Number/README.md
new file mode 100644
index 00000000..e51ab250
--- /dev/null
+++ b/Algorithms/2.Add-Two-Number/README.md
@@ -0,0 +1,30 @@
+# [2. Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)
+
+## 题目
+
+You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
+
+You may assume the two numbers do not contain any leading zero, except the number 0 itself.
+
+Example:
+
+```
+Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
+Output: 7 -> 0 -> 8
+```
+Explanation: 342 + 465 = 807.
+
+
+## 题目大意
+
+2 个逆序的链表，要求从低位开始相加，得出结果也逆序输出，返回值是逆序结果链表的头结点。
+
+需要注意的是各种进位问题。
+
+极端情况，例如
+```
+Input: (9 -> 9 -> 9 -> 9 -> 9) + (1 -> )
+Output: 0 -> 0 -> 0 -> 0 -> 0 -> 1
+```
+
+为了处理方法统一，可以先建立一个虚拟头结点，这个虚拟头结点的 Next 指向真正的 head，这样 head 不需要单独处理，直接 while 循环即可。另外判断循环终止的条件不用是 p.Next ！= nil，这样最后一位还需要额外计算，循环终止条件应该是 p != nil。
\ No newline at end of file