# Javascript in Leetcode 07–09 | 面試問題

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### 7. Reverse Integer

Given a signed 32-bit integer `x`

, return `x`

* with its digits reversed*. If reversing `x`

causes the value to go outside the signed 32-bit integer range `[-231, 231 - 1]`

, then return `0`

.

**Assume the environment does not allow you to store 64-bit integers (signed or unsigned).**

**Example 1:**

Input: x = 123 Output: 321

**Example 2:**

Input: x = -123 Output: -321

**Example 3:**

Input: x = 120 Output: 21

**Constraints:**

`-231 <= x <= 231 - 1`

### 8. String to Integer (atoi)

Implement the `myAtoi(string s)`

function, which converts a string to a 32-bit signed integer (similar to C/C++'s `atoi`

function).

The algorithm for `myAtoi(string s)`

is as follows:

- Read in and ignore any leading whitespace.
- Check if the next character (if not already at the end of the string) is
`'-'`

or`'+'`

. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present. - Read in next the characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.
- Convert these digits into an integer (i.e.
`"123" -> 123`

,`"0032" -> 32`

). If no digits were read, then the integer is`0`

. Change the sign as necessary (from step 2). - If the integer is out of the 32-bit signed integer range
`[-231, 231 - 1]`

, then clamp the integer so that it remains in the range. Specifically, integers less than`-231`

should be clamped to`-231`

, and integers greater than`231 - 1`

should be clamped to`231 - 1`

. - Return the integer as the final result.

**Note:**

- Only the space character
`' '`

is considered a whitespace character. **Do not ignore**any characters other than the leading whitespace or the rest of the string after the digits.

**Example 1:**

Input: s = "42" Output: 42 Explanation: The underlined characters are what is read in, the caret is the current reader position. Step 1: "42" (no characters read because there is no leading whitespace) ^ Step 2: "42" (no characters read because there is neither a '-' nor '+') ^ Step 3: "42" ("42" is read in) ^ The parsed integer is 42. Since 42 is in the range [-231, 231 - 1], the final result is 42.

**Example 2:**

Input: s = " -42" Output: -42 Explanation: Step 1: " -42" (leading whitespace is read and ignored) ^ Step 2: " -42" ('-' is read, so the result should be negative) ^ Step 3: " -42" ("42" is read in) ^ The parsed integer is -42. Since -42 is in the range [-231, 231 - 1], the final result is -42.

**Example 3:**

Input: s = "4193 with words" Output: 4193 Explanation: Step 1: "4193 with words" (no characters read because there is no leading whitespace) ^ Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+') ^ Step 3: "4193 with words" ("4193" is read in; reading stops because the next character is a non-digit) ^ The parsed integer is 4193. Since 4193 is in the range [-231, 231 - 1], the final result is 4193.

**Constraints:**

`0 <= s.length <= 200`

`s`

consists of English letters (lower-case and upper-case), digits (`0-9`

),`' '`

,`'+'`

,`'-'`

, and`'.'`

.

### 9. Palindrome Number

Given an integer `x`

, return `true`

if `x`

is palindrome integer.

An integer is a **palindrome** when it reads the same backward as forward.

- For example,
`121`

is a palindrome while`123`

is not.

**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.

**Constraints:**

`-231 <= x <= 231 - 1`

**Follow up:** Could you solve it without converting the integer to a string?

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