Add solution 989

leetcode/0989.Add-to-Array-Form-of-Integer/README.md

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+# [989. Add to Array-Form of Integer](https://leetcode.com/problems/add-to-array-form-of-integer/)
+
+## 题目
+
+For a non-negative integer `X`, the *array-form of `X`* is an array of its digits in left to right order.  For example, if `X = 1231`, then the array form is `[1,2,3,1]`.
+
+Given the array-form `A` of a non-negative integer `X`, return the array-form of the integer `X+K`.
+
+**Example 1:**
+
+```
+Input: A = [1,2,0,0], K = 34
+Output: [1,2,3,4]
+Explanation: 1200 + 34 = 1234
+```
+
+**Example 2:**
+
+```
+Input: A = [2,7,4], K = 181
+Output: [4,5,5]
+Explanation: 274 + 181 = 455
+```
+
+**Example 3:**
+
+```
+Input: A = [2,1,5], K = 806
+Output: [1,0,2,1]
+Explanation: 215 + 806 = 1021
+```
+
+**Example 4:**
+
+```
+Input: A = [9,9,9,9,9,9,9,9,9,9], K = 1
+Output: [1,0,0,0,0,0,0,0,0,0,0]
+Explanation: 9999999999 + 1 = 10000000000
+```
+
+**Note：**
+
+1. `1 <= A.length <= 10000`
+2. `0 <= A[i] <= 9`
+3. `0 <= K <= 10000`
+4. If `A.length > 1`, then `A[0] != 0`
+
+## 题目大意
+
+对于非负整数 X 而言，X 的数组形式是每位数字按从左到右的顺序形成的数组。例如，如果 X = 1231，那么其数组形式为 [1,2,3,1]。给定非负整数 X 的数组形式 A，返回整数 X+K 的数组形式。
+
+## 解题思路
+
+- 简单题，计算 2 个非负整数的和。累加过程中不断的进位，最终输出到数组中记得需要逆序，即数字的高位排在数组下标较小的位置。
+
+## 代码
+
+```go
+package leetcode
+
+func addToArrayForm(A []int, K int) []int {
+	res := []int{}
+	for i := len(A) - 1; i >= 0; i-- {
+		sum := A[i] + K%10
+		K /= 10
+		if sum >= 10 {
+			K++
+			sum -= 10
+		}
+		res = append(res, sum)
+	}
+	for ; K > 0; K /= 10 {
+		res = append(res, K%10)
+	}
+	reverse(res)
+	return res
+}
+
+func reverse(A []int) {
+	for i, n := 0, len(A); i < n/2; i++ {
+		A[i], A[n-1-i] = A[n-1-i], A[i]
+	}
+}
+```