Leetcode 88. Merge Sorted Array (Easy)

Leetcode Top Interview 150 的其中一題

題目描述

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function, but instead be stored inside the array nums1. To accommodate this, nums1 has a length of m + n, where the first m elements denote the elements that should be merged, and the last n elements are set to 0 and should be ignored.nums2 has a length of n.

範例

Example 1:

Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
Output: [1,2,2,3,5,6]
Explanation: The arrays we are merging are [1,2,3] and [2,5,6].
The result of the merge is [1,2,2,3,5,6] with the underlined elements coming from nums1.

Example 2:

Input: nums1 = [1], m = 1, nums2 = [], n = 0
Output: [1]
Explanation: The arrays we are merging are [1] and [].
The result of the merge is [1].

Example 3:

Input: nums1 = [0], m = 0, nums2 = [1], n = 1
Output: [1]
Explanation: The arrays we are merging are [] and [1].
The result of the merge is [1].
Note that because m = 0, there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1.

Constraints

• nums1.length == m + n
• nums2.length == n
• 0 <= m, n <= 200
• 1 <= m + n <= 200
• -10^9 <= nums1[i], nums2[j] <= 10^9

Follow up: Can you come up with an algorithm that runs in O(m + n) time?

解法

解法一

第一個解法有點簡單暴力，把 nums2 的值放到nums1 後段後，直接做排序

func merge(nums1 []int, m int, nums2 []int, n int)  {
    for j := m; j < len(nums1); j++ {
        nums1[j] = nums2[j-m]
    }

    sort.Ints(nums1)
}

解法二

這個解法很巧妙！因為 nums1 最後 n 格是空的，所以我們可以從 nums1 有數值的地方的尾巴(nums1最大的值) 和 nums2 最大的值開始比較，把比較大的填到 nums1 的最後，以此類推，從大的開始填

func merge(nums1 []int, m int, nums2 []int, n int)  {
    k := m+n-1 //最後一格
    i := m-1
    j := n-1

    for j>=0 {
        if i >= 0 && (nums1[i] > nums2[j]) {
            nums1[k] = nums1[i]
            i--
        } else {
            nums1[k] = nums2[j]
            j--
        }
        k--
    }
} 

Request body is undefined

在試著打自己寫的 api 時，發現 Body 明明有以 JSON 的方式傳遞，使用 fetch function 打出去的時候，對面卻找不到Body，後來發現是兩個原因：

1. express 少了 app.use(express.json())
2. fetch function 的 Header 少了 "Content-Type": "application/json"

Typescript - tsconfig.json - Build:No inputs were found in config file

出現這個錯誤的解決辦法：

在 tsconfig.json 的 compilerOptions 中加上一行：

"compilerOptions": {
    "allowJs": true,
}

Go - postgresql - LastInsertId is not supported by this driver

在執行下面程式碼的時候：

sqlStatement := `INSERT INTO tx (urls) VALUES($1) RETURNING id`
res, err := db.Exec(sqlStatement, pq.Array(body.Urls))
id, err := res.LastInsertId()

出現下面錯誤： LastInsertId is not supported by this driver 這是因為 LastInsertId() 不支援 Postgresql driver

解決方式

將程式碼改為如下：

sqlStatement := `INSERT INTO tx (urls) VALUES($1) RETURNING id`
var id int
err = db.QueryRow(sqlStatement, pq.Array(body.Urls)).Scan(&id)

Typeorm Error - Cannot find module

在寫完 seed file 做執行的時候，卻出現下列錯誤：

Error: Cannot find module

這是因為在 seed.ts 內引入 entity 時的路徑關係 正確寫法：

import Flight from '../entity/Flight'

錯誤寫法：

import Flight from 'db/entity/Flight'

應使用相對路徑而非絕對路徑。