LeetCode 167. Two Sum II - Input Array Is Sorted

 https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/

題目是Input是一個陣列，且經過小到大的排序，需要將兩數相加，回傳該兩數的位置+1，且兩個位置不能相同。

Example 1:

Input: numbers = [2,7,11,15], target = 9

Output: [1,2]

Explanation: The sum of 2 and 7 is 9. Therefore, index1 = 1, index2 = 2. We return [1, 2].

Example 2:

Input: numbers = [2,3,4], target = 6

Output: [1,3]

Explanation: The sum of 2 and 4 is 6. Therefore index1 = 1, index2 = 3. We return [1, 3].

Example 3:

Input: numbers = [-1,0], target = -1

Output: [1,2]

Explanation: The sum of -1 and 0 is -1. Therefore index1 = 1, index2 = 2. We return [1, 2].

解題：

一開始用最直觀的暴力解

LeetCode 9. Palindrome Number

 https://leetcode.com/problems/palindrome-number/

給定一個數字，假如數字從頭到中間和從中間到末端是一樣的

回傳 true，反之回傳 false

範例：

Example 1:

Input: x = 121

Output: true

Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

Input: x = -121

Output: false

Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: x = 10

Output: false

Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

進階解題，建議不要用字串型別來解此題

解題答案

我先直接判斷是否為 0 , 是否為負數, 判斷是否為偶數長度, 是否為奇數長度

LeetCode 13. Roman to Integer

https://leetcode.com/problems/roman-to-integer/

題目是將羅馬文字轉成數字

Symbol Value

I 1

V 5

X 10

L 50

C 100

D 500

M 1000

For example, 2 is written as II in Roman numeral, just two one's added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

I can be placed before V (5) and X (10) to make 4 and 9.

X can be placed before L (50) and C (100) to make 40 and 90.

C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer.

LeetCode 1. Two Sum

 https://leetcode.com/problems/two-sum/

題目是Input是一個陣列，且沒有排序，需要將兩數相加，回傳該兩數的位置，且兩個位置不能相同。

範例：

Example 1:

Input: nums = [2,7,11,15], target = 9

Output: [0,1]

Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6

Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6

Output: [0,1]

解題：

LeetCode 14. Longest Common Prefix

https://leetcode.com/problems/longest-common-prefix/

題目：

Write a function to find the longest common prefix string amongst an array of strings.
        
If there is no common prefix, return an empty string "".

Example 1:

Input: strs = ["flower","flow","flight"]
Output: "fl"
        
Example 2:

Input: strs = ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.


Constraints:
1 <= strs.length <= 200
0 <= strs[i].length <= 200
strs[i] consists of only lower-case English letters.