Product of Array Except Self

pullrequests/product_of_array_except_self/step1.go

@@ -0,0 +1,35 @@
+//lint:file-ignore U1000 Ignore all unused code
+package template
+
+/*
+時間：６分
+全体の積を求め、個々の数字で割ることで求める。
+解いた後に割り算を使ってはいけないということに気づいた。
+*/
+func productExceptSelfStep1(nums []int) []int {
+	allProduct, zeroCount := 0, 0
+	for _, n := range nums {
+		if n == 0 {
+			zeroCount++
+			continue
+		}
+		if allProduct == 0 {
+			allProduct = n
+		} else {
+			allProduct *= n
+		}
+	}
+	products := make([]int, len(nums))
+	for i := range products {
+		if zeroCount > 0 {
+			if nums[i] == 0 && zeroCount == 1 {
+				products[i] = allProduct
+			} else {
+				products[i] = 0
+			}
+		} else {
+			products[i] = allProduct / nums[i]
+		}
+	}
+	return products
+}

pullrequests/product_of_array_except_self/step2.go

@@ -0,0 +1,20 @@
+//lint:file-ignore U1000 Ignore all unused code
+package template
+
+/*
+他の人の解法を見て書いた。
+*/
+func productExceptSelfStep2(nums []int) []int {
+	products := make([]int, len(nums))
+	leftProduct := 1
+	for i := 0; i < len(nums); i++ {
+		products[i] = leftProduct
+		leftProduct *= nums[i]
+	}
+	rightProduct := 1
+	for i := len(nums) - 1; i >= 0; i-- {
+		products[i] *= rightProduct
+		rightProduct *= nums[i]
+	}
+	return products
+}