Reverse Integer

You can reverse the integer by converting it into a string, reversing the string, and then converting it back to an integer, keeping in mind the constraints of the 32-bit signed integer range. Here’s the code snippet:

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class Solution:
    def reverse(self, x: int) -> int:
        INT_MAX = 2**31 - 1
        INT_MIN = -2**31

        # Handle negative numbers
        sign = -1 if x < 0 else 1

        # Reverse the absolute value and multiply by the sign
        reversed_x = sign * int(str(abs(x))[::-1])

        # Check if the reversed integer is outside the 32-bit signed integer range
        if reversed_x < INT_MIN or reversed_x > INT_MAX:
            return 0

        return reversed_x

Explanation:

  1. Determine the sign of the integer and take the absolute value.
  2. Convert the absolute value to a string, reverse it, and then convert it back to an integer.
  3. Multiply the reversed integer by the original sign.
  4. Check if the reversed integer is outside the 32-bit signed integer range, and if so, return 0.

This code takes care of the edge cases and returns the reversed integer, or 0 if the reversed integer falls outside the valid range.

Identifying Problem Isomorphism

“Reverse Integer” can be approximately mapped to the following problems:

  1. “Palindrome Number” (#9) on LeetCode
  2. “Plus One” (#66) on LeetCode

Reasoning:

These problems involve operations on numerical digits in some form, which is a commonality with the problem “Reverse Integer”.

  1. “Palindrome Number” is a more complex problem compared to “Reverse Integer”. It involves checking whether a number remains the same when its digits are reversed. So, it involves the concept of reversing the digits of a number just like in the “Reverse Integer” problem, but adds the complexity of checking for the palindrome property.

  2. “Plus One” is a simpler problem compared to “Reverse Integer”. The problem asks to add one to the number represented as an array of digits. The operation of manipulating the digits is common with the problem “Reverse Integer”, but “Plus One” does not require reversing the digits.

While these problems are not exact isomorphs of “Reverse Integer”, they involve similar operations or checks to be performed on numerical digits.

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class Solution:
    # @return an integer
    def reverse(self, x):
        result = 0

        if x < 0:
            symbol = -1
            x = -x
        else:
            symbol = 1

        while x:
            result = result * 10 + x % 10
            x /= 10

        return 0 if result > pow(2, 31) else result * symbol

Language Agnostic Coding Drills

Here are the smallest units of learning that you can code separately:

Drill 1 - Basic Arithmetic Operators:

Understanding basic arithmetic operators such as addition, subtraction, multiplication, and division. These are required for operations such as calculating the modulus and dividing by 10.

Task: Practice using the arithmetic operators with various numbers.

Drill 2 - Comparison Operators:

Understanding comparison operators such as greater than, less than, equals, not equals.

Task: Practice using the comparison operators with various numbers.

Drill 3 - Using Variables:

Understanding how to declare and use variables. The x and result variables are used to store the input number and the reversed number, respectively.

Task: Practice declaring variables and assigning them different values.

Drill 4 - Conditionals:

Understanding how to use conditionals. This is needed to check if x is less than zero and to decide whether the final result is greater than 2^31.

Task: Write a program that prints different messages based on the value of a variable.

Drill 5 - While Loops:

Understanding how to use while loops. The loop is used to continually divide x by 10 until x becomes 0.

Task: Write a program that prints the numbers from 1 to 10 using a while loop.

Drill 6 - Power Function:

Understanding how to use the power function. This is used to calculate 2^31.

Task: Write a program that calculates and prints the square of various numbers.

Drill 7 - Combining Everything:

Understanding how to put all the above concepts together to solve a problem.

Task: Implement the reverse function.

By working through these drills, you can separately code each concept, and then combine them into the final solution for reversing an integer. These drills are ordered in increasing level of difficulty, starting from understanding basic operators to combining everything to solve a problem.

Targeted Drills in Python

Here are Python coding drills corresponding to each of the steps:

Drill 1 - Basic Arithmetic Operators:

Task: Practice using the arithmetic operators with various numbers.

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# Add two numbers
print(5 + 3)

# Subtract two numbers
print(10 - 7)

# Multiply two numbers
print(4 * 2)

# Divide two numbers
print(9 / 3)

Drill 2 - Comparison Operators:

Task: Practice using the comparison operators with various numbers.

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# Compare two numbers
print(5 > 3)
print(10 < 7)
print(4 == 2)
print(9 != 3)

Drill 3 - Using Variables:

Task: Practice declaring variables and assigning them different values.

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# Declare a variable
x = 5

# Use the variable
print(x * 2)

Drill 4 - Conditionals:

Task: Write a program that prints different messages based on the value of a variable.

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# Use a conditional
x = 5
if x > 0:
    print("x is positive")
else:
    print("x is non-positive")

Drill 5 - While Loops:

Task: Write a program that prints the numbers from 1 to 10 using a while loop.

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# Use a while loop
x = 1
while x <= 10:
    print(x)
    x += 1

Drill 6 - Power Function:

Task: Write a program that calculates and prints the square of various numbers.

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# Use the power function
for i in range(1, 11):
    print(pow(i, 2))

Drill 7 - Combining Everything:

Task: Implement the reverse function.

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def reverse(x):
    result = 0

    if x < 0:
        symbol = -1
        x = -x
    else:
        symbol = 1

    while x:
        result = result * 10 + x % 10
        x //= 10

    return 0 if result > pow(2, 31) else result * symbol

print(reverse(-123))