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• 7. Reverse Integer
• 9. Palindrome Number
• 43. Multiply Strings
• 50. Pow(x, n)
• 65 . Valid Number
• 66. Plus One
• 149 . Max Points on a Line
• 166 . Fraction to Recurring Decimal
• 168 . Excel Sheet Column Title
• 171. Excel Sheet Column Number
• 172. Factorial Trailing Zeroes
• 179 . Largest Number
• 224. Basic Calculator
• 227 . Basic Calculator II
• 233 . Number of Digit One
• 273. Integer to English Words

### 7. Reverse Integer

Example 1:

Example 2:

Example 3:

Note: Assume we are dealing with an environment which could only hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

C++

Java

Python

python 负数的除法和C++/ java不同。需要先转成整数。

### 9. Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.

C++

Python

### 43. Multiply Strings

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2.

Note:

The length of both num1 and num2 is < 110. Both num1 and num2 contains only digits 0-9. Both num1 and num2 does not contain any leading zero. You must not use any built-in BigInteger library or convert the inputs to integer directly.

C++ 9ms

Python

C++ 版本2

### 50. leetcode Pow(x, n)

Implement pow(x, n).

Example 1:

Input: 2.00000, 10 Output: 1024.00000

Example 2:

Input: 2.10000, 3 Output: 9.26100

C++

Python

### 65. leetcode Valid Number

Validate if a given string is numeric.

Some examples: "0" => true " 0.1 " => true "abc" => false "1 a" => false "2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

1. 开始和结束可以有若干个空格
2. 数字最开始前面可能有+ 或者-号
3. 指数 e前面要有数字，之后的数字必须为整数，e后面可能有一个+或者-号
4. ' . '前或者后要有数字。不能单纯的一个点。

• 如果s[i]不是数字：

• s[i]=='e' 之前不能出现e，之前必须有数字。并且判断下一个数是否为'+' or  '-'
• s[i]=='.'   .之前不能有. ， 并且 e没有出现（否则为如5e6.5这种形式）
• return false
• s[i]是数字：

• 标记e和p之前出现了数字
• 根据e和p是否出现标记之后是否出现数字。
• 扫描数组完毕，需对e之后是否有数字和p之前或者之后是否有数字进行判断。

C++

Python

### 66. Plus One

Given a non-negative number represented as an array of digits, plus one to the number.

The digits are stored such that the most significant digit is at the head of the list.

C++

Python

Given two binary strings, return their sum (also a binary string).

For example, a = "11" b = "1" Return "100".

C++

Python

### 149. Max Points on a Line

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.

• i和j坐标相等，标记同样的点+1
• i和j横坐标相等，标记斜率无穷大+1
• i和j横坐标不相等，计算斜率

### 166. Fraction to Recurring Decimal

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.

If the fractional part is repeating, enclose the repeating part in parentheses.

For example,

• Given numerator = 1, denominator = 2, return "0.5".
• Given numerator = 2, denominator = 1, return "2".
• Given numerator = 2, denominator = 3, return "0.(6)".

### 168. Excel Sheet Column Title

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

### 171. Excel Sheet Column Number

Related to question Excel Sheet Column Title

Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

### 172. Factorial Trailing Zeroes

Given an integer n, return the number of trailing zeroes in n!.

Note: Your solution should be in logarithmic time complexity.

### 179. Largest Number

Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.

Note: The result may be very large, so you need to return a string instead of an integer.

C++

Java

Python

### 224. Basic Calculator

Implement a basic calculator to evaluate a simple expression string.

The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty spaces .

You may assume that the given expression is always valid.

Some examples:

Note: Do not use the eval built-in library function.

Python

### 227. Basic Calculator II

Implement a basic calculator to evaluate a simple expression string.

The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.

You may assume that the given expression is always valid.

Some examples:

Note: Do not use the eval built-in library function.

Python

### 233. Number of Digit One

Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.

For example: Given n = 13, Return 6, because digit 1 occurred in the following numbers: 1, 10, 11, 12, 13.

Hint:

1. Beware of overflow.

• 3 -> 1
• 33 -> 10 + 3 * 1 + 1= 14 （1X的情况加上1~30的情况，加上不到40然而有一个31多了一个）
• 133  -> 34 + 20 + 14

• 233 -> 100 + 20*2 +14 = 154

C++

Python

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

For example:

Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it.

Follow up: Could you do it without any loop/recursion in O(1) runtime?

C++

Python

Python

C++

Python

### 273. Integer to English Words

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.

For example,

Hint:

1. Did you see a pattern in dividing the number into chunk of words? For example, 123 and 123000.
2. Group the number by thousands (3 digits). You can write a helper function that takes a number less than 1000 and convert just that chunk to words.
3. There are many edge cases. What are some good test cases? Does your code work with input such as 0? Or 1000010? (middle chunk is zero and should not be printed out)