add 238 solution

Author: halfrost

README.md

@@ -375,7 +375,7 @@
 |0235|Lowest Common Ancestor of a Binary Search Tree|[Go](https://github.com/halfrost/LeetCode-Go/tree/master/leetcode/0235.Lowest-Common-Ancestor-of-a-Binary-Search-Tree)|60.1%|Medium||
 |0236|Lowest Common Ancestor of a Binary Tree|[Go](https://github.com/halfrost/LeetCode-Go/tree/master/leetcode/0236.Lowest-Common-Ancestor-of-a-Binary-Tree)|57.9%|Medium||
 |0237|Delete Node in a Linked List|[Go](https://github.com/halfrost/LeetCode-Go/tree/master/leetcode/0237.Delete-Node-in-a-Linked-List)|75.1%|Medium||
-|0238|Product of Array Except Self||64.7%|Medium||
+|0238|Product of Array Except Self|[Go](https://github.com/halfrost/LeetCode-Go/tree/master/leetcode/0238.Product-of-Array-Except-Self)|64.7%|Medium||
 |0239|Sliding Window Maximum|[Go](https://github.com/halfrost/LeetCode-Go/tree/master/leetcode/0239.Sliding-Window-Maximum)|46.6%|Hard||
 |0240|Search a 2D Matrix II|[Go](https://github.com/halfrost/LeetCode-Go/tree/master/leetcode/0240.Search-a-2D-Matrix-II)|50.5%|Medium||
 |0241|Different Ways to Add Parentheses||63.1%|Medium||

leetcode/0238.Product-of-Array-Except-Self/238. Product of Array Except Self.go

@@ -0,0 +1,19 @@
+package leetcode
+
+// 解法一 前缀积 * 后缀积。不使用除法，时间复杂度 O(n)，除输出数组外空间复杂度 O(1)。
+func productExceptSelf(nums []int) []int {
+	n := len(nums)
+	res := make([]int, n)
+	// res[i] 先存 nums[i] 左边所有元素的乘积
+	res[0] = 1
+	for i := 1; i < n; i++ {
+		res[i] = res[i-1] * nums[i-1]
+	}
+	// 再从右往左乘上 nums[i] 右边所有元素的乘积，right 累计后缀积
+	right := 1
+	for i := n - 1; i >= 0; i-- {
+		res[i] *= right
+		right *= nums[i]
+	}
+	return res
+}

leetcode/0238.Product-of-Array-Except-Self/238. Product of Array Except Self_test.go

@@ -0,0 +1,68 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question238 struct {
+	para238
+	ans238
+}
+
+// para is the parameter
+// one represents the first parameter
+type para238 struct {
+	one []int
+}
+
+// ans is the answer
+// one represents the first answer
+type ans238 struct {
+	one []int
+}
+
+func Test_Problem238(t *testing.T) {
+
+	qs := []question238{
+
+		{
+			para238{[]int{1, 2, 3, 4}},
+			ans238{[]int{24, 12, 8, 6}},
+		},
+
+		{
+			para238{[]int{-1, 1, 0, -3, 3}},
+			ans238{[]int{0, 0, 9, 0, 0}},
+		},
+
+		{
+			para238{[]int{2, 3}},
+			ans238{[]int{3, 2}},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 238------------------------\n")
+
+	for _, q := range qs {
+		a, p := q.ans238, q.para238
+		got := productExceptSelf(p.one)
+		fmt.Printf("【input】:%v       【output】:%v\n", p, got)
+		if !equal238(got, a.one) {
+			t.Fatalf("input %v: expected %v, got %v", p.one, a.one, got)
+		}
+	}
+	fmt.Printf("\n\n\n")
+}
+
+func equal238(a, b []int) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}