Max Consecutive Ones

Finding the maximum number of consecutive 1’s in a binary array can be solved using a simple iteration through the array. We’ll use two variables: one to keep track of the current count of consecutive 1’s and another to keep track of the maximum count found so far.

Algorithm:

  1. Initialize Variables: Initialize two variables, current_count and max_count, both set to 0.
  2. Iterate through the Array: Iterate through each element in the binary array nums.
    • If the current element is 1, increment current_count.
    • If the current element is 0, update max_count if current_count is greater than max_count, then reset current_count to 0.
  3. Check Last Segment: After the loop, check if the current count is greater than the maximum count, as the array might end with a sequence of 1’s.
  4. Return Result: Return the value of max_count.

Here’s the code:

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class Solution:
    def findMaxConsecutiveOnes(self, nums: List[int]) -> int:
        current_count = 0
        max_count = 0

        for num in nums:
            if num == 1:
                current_count += 1
            else:
                max_count = max(max_count, current_count)
                current_count = 0
        
        # Check if the array ends with a sequence of 1's
        max_count = max(max_count, current_count)
        
        return max_count

This code would produce the result 3 for the input nums = [1,1,0,1,1,1], as the maximum number of consecutive 1’s is 3.

  1. Input is an array Output is an integer (maximum consequetive numbers)

  2. Only 1 and 0s

  3. n = 0 return 0 Just one element, n = 1 return 1 if it is 1 otherwise 0

Time: O(n ) Space: O(1)

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# @param {Integer[]} nums
# @return {Integer}


def find_max_consecutive_ones(nums)
    result = 0
    count = 0

    for i in (0..nums.size-1)
        if nums[i] == 1
           count += 1 
        else
            count = 0
        end
        result = [result, count].max
    end

    return result
end

Identifying Problem Isomorphism

“Max Consecutive Ones” involves finding the maximum number of consecutive 1s in a given binary array.

Two problems that could be considered isomorphic are:

  1. “Run Length Encoding”: This problem is simpler than “Max Consecutive Ones”. In Run Length Encoding, you convert a sequence into a series of data elements and counts. Each count indicates the number of times a data element is repeated. In the context of “Max Consecutive Ones”, you can think of the binary array as a sequence, and each count would indicate the number of consecutive 1s or 0s.

  2. “Max Consecutive Ones II”: This problem is more complex. It extends the problem by allowing you to flip at most one ‘0’ to ‘1’ to achieve the longest sequence of consecutive 1s.

The order from simple to more complex would be:

  • “Run Length Encoding”
  • “Max Consecutive Ones”
  • “Max Consecutive Ones II”

All of these problems involve handling consecutive elements in an array, but with varying degrees of complexity.

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class Solution:
    def findMaxConsecutiveOnes(self, nums: List[int]) -> int:
        count = maxCount = 0

        for i in range(len(nums)):
            if nums[i] == 1:
                count += 1
            else:
                maxCount = max(count, maxCount)
                count = 0

        return max(count, maxCount)

Problem Classification

This problem falls under the “Algorithms and Data Structures” domain, specifically “Array Manipulation” and “Searching and Tracking”.

**The ‘What’:

  • You’re given a binary array (an array that only contains 0s and 1s).
  • You’re asked to find the maximum number of consecutive 1s in the array.

The problem can be classified into:

  • Searching: You are essentially searching for the longest sequence of 1s in the array.
  • Tracking: You need to track the longest sequence encountered so far and the current sequence of consecutive 1s.
  • Array Manipulation: You are working with a binary array, traversing it, and dealing with its elements.

This problem is a “Searching and Tracking within Array Manipulation” problem.

Language Agnostic Coding Drills

  1. Class and Function Declaration (Difficulty: Easy): The very first step is understanding how to declare a class and a function in Python. In this case, the class Solution has a method findMaxConsecutiveOnes.

  2. List Iteration (Difficulty: Easy): This concept involves looping over each item in the list nums. The for loop is used here to iterate over the list.

  3. Condition Checking (Difficulty: Easy): The if-else statement is used here to check whether the current number is 1 or not.

  4. Counter Manipulation (Difficulty: Medium): This involves incrementing the counter variable count when certain conditions are met and resetting it when they aren’t. This concept is crucial to track the length of the current sequence of 1s.

  5. Comparison and Variable Updating (Difficulty: Medium): This involves comparing two variables (count and maxCount) and updating one of them based on the result of the comparison. In the problem, we need to keep track of the maximum sequence of consecutive 1s encountered so far, and thus we keep updating maxCount if a larger sequence is found.

  6. Return Statement (Difficulty: Easy): This involves returning the final result, which in this case is the maximum of count and maxCount.

The problem-solving strategy that this code employs starts with initializing two counters to zero: one to track the length of the current sequence of consecutive 1s (count), and another to keep track of the maximum sequence length seen so far (maxCount). It then goes through each element in the list, incrementing count when a 1 is encountered, and updating maxCount and resetting count when a 0 is encountered. After going through all the elements, it ensures the last sequence of 1s is considered by returning the maximum of count and maxCount.

The process can be seen as a combination of the basic coding drills: class and function declaration, list iteration, condition checking, counter manipulation, comparison and variable updating, and the use of a return statement. Each drill builds upon the previous one to form the final solution.

Targeted Drills in Python

  1. Class and Function Declaration: Create a Python class with a single method.

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    class MySolution:
    def myFunction(self):
        pass

  2. List Iteration: Write a Python function that iterates over a list of integers.

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    def iterate_over_list(nums):
    for num in nums:
        print(num)

To run the code you’ve provided, you first need to create an instance of the class Solution, then call the iterate_over_list method on that instance. Here’s an example:

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class Solution:
    def iterate_over_list(self, nums):  # added self as first parameter
        for n in nums:
            print(n)

# Create an instance of Solution
solution_instance = Solution()

# Call the method iterate_over_list
solution_instance.iterate_over_list([1, 2, 3, 4, 5])

This will print out:

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5

It’s important to note that I added self as the first parameter of the iterate_over_list method. This is necessary in Python because the methods of a class need to know which instance of the class they are dealing with. The self parameter is automatically filled in by Python to refer to the instance of the class (in this case, solution_instance). This is similar to this in some other languages.

Also, the way to run the code might depend on the environment you’re using. In a file, you’d typically put this code and then run the file using a Python interpreter (like typing python myfile.py in a terminal). In an interactive environment like a Python REPL or Jupyter notebook, you can usually just run the code directly.

  1. Condition Checking: Write a function that checks if a number is equal to 1 and prints a message.

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    def check_number(num):
    if num == 1:
        print("The number is 1.")
    else:
        print("The number is not 1.")

  2. Counter Manipulation: Write a function that counts the number of 1s in a given list.

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    def count_ones(nums):
    count = 0
    for num in nums:
        if num == 1:
            count += 1
    return count

Frequency Counter.

  1. Comparison and Variable Updating: Write a function that finds the maximum number in a list.

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    def find_max(nums):
    max_num = nums[0]
    for num in nums:
        if num > max_num:
            max_num = num
    return max_num

  2. Return Statement: Write a function that returns the sum of a list of numbers.

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    def find_sum(nums):
    total = sum(nums)
    return total

To address problem-specific needs, we can write a function that finds the maximum number of consecutive 1s in a binary list:

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def max_consecutive_ones(nums):
    count = max_count = 0
    for num in nums:
        if num == 1:
            count += 1
        else:
            max_count = max(max_count, count)
            count = 0
    return max(max_count, count)

Each of these drills builds a foundational understanding of the concepts used in the final solution. When all the drills are combined and customized according to the problem needs, they lead to the complete solution as demonstrated in max_consecutive_ones().

Python Basics

Pass

In Python, the pass statement is a placeholder statement that is used when the syntax requires a statement, but where you don’t want any command or code to be executed.

This can be useful in a variety of situations. For instance, it allows you to create a class or a function that doesn’t do anything (yet):

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def some_function():
    pass  # TODO: implement this function

class SomeClass:
    pass  # TODO: implement this class

The pass statement is basically a “do nothing” operation. It’s only required because Python’s syntax needs something there, and is often used as a placeholder to remind the developer to implement something at a later point.

Colon

In Python, the colon : is not associated with the use of a tab or indentation. It is instead used to introduce a new block of code (a suite), usually after statements like if, else, elif, while, for, def, class, try, except, etc. Here are a few examples:

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if condition:    # Notice the colon here
    # This block of code will run if condition is True
    print("Condition is true")

for i in range(5):    # Notice the colon here
    # This block of code will run five times
    print(i)

def func():    # Notice the colon here
    # This is a function definition.
    pass

The indentation (done with tabs or spaces) that follows the colon is used to denote the block of code that is controlled by the statement ending with a colon.

So in short, you don’t need to use a colon at the end of every line that uses a tab, but you do need to use a colon to denote the start of a new block of code (like a loop, conditional statement, function, etc), and that block of code should be indented for clarity and to avoid syntax errors.

In Python, after a colon (:), the subsequent lines that are part of the same code block should be indented. It’s not strictly required to be a tab. It can be a certain number of spaces. The key thing is to be consistent with your choice of indentation throughout your code.

Python does not require a specific number of spaces for indentation, but the typical convention is to use four spaces for each level of indent. Here’s an example:

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def function():  # colon indicates start of function definition block
    print("This line is indented")  # this line is indented with 4 spaces or a tab
    
    if True:  # colon indicates start of if statement block
        print("This line is indented twice")  # this line is indented with 8 spaces or 2 tabs

If you are using an integrated development environment (IDE) or a text editor like Visual Studio Code, it usually handles this for you. When you press enter after typing a colon, it will automatically indent the next line.

Remember, consistent indentation is not just about style in Python, it is required for your code to run correctly. Mixing tabs and spaces for indentation can lead to errors.

In Python, the colon (:) is used in several cases to denote the start of a block of code. Here are the main instances where you would need to use a colon:

  1. Defining a function or a class: When you’re defining a function with def or a class with class, you end the line with a colon to start the block of code that makes up the body of the function or class.
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def my_function():
    # function body starts here

class MyClass:
    # class body starts here
  1. Control flow statements: This includes if, elif, else, while, for, and try, except, finally. They all need a colon at the end of the line to start the block of code that is controlled by them.
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if condition:
    # if block starts here

for i in my_list:
    # for block starts here

while condition:
    # while block starts here

try:
    # try block starts here
except Exception:
    # exception block starts here
finally:
    # finally

### The Missing self

```python
class Solution:
    def iterate_over_list(nums):
        for n in nums:
            print(n)

solution = Solution()
solution.iterate_over_list([1, 2, 3, 4, 5])

The error in your code is due to the missing self parameter in the definition of your iterate_over_list method.

In Python, instance methods need a reference to the instance of the class itself. This is provided by including self as the first parameter in the method definition. This allows you to access other attributes or methods within the class.

Here is the corrected version of your code:

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class Solution:
    def iterate_over_list(self, nums):  # Notice the 'self' parameter here.
        for n in nums:
            print(n)

solution = Solution()
solution.iterate_over_list([1, 2, 3, 4, 5])

Error:

    solution.iterate_over_list([1, 2, 3, 4, 5])
TypeError: Solution.iterate_over_list() takes 1 positional argument but 2 were given

When you call solution.iterate_over_list([1, 2, 3, 4, 5]), Python automatically passes the solution instance as the first argument to the method. That’s why you need to include self in your method definition.

In short, self is used to refer to the instance of the class and allows access to its attributes and methods. This is similar to how this is used in some other programming languages.

Braces and Colon

It looks like the braces is replace by colon for the starting brace and indentation for closing brace in Python, is this correct?

Yes, that’s correct. Python uses indentation to denote blocks of code that are part of control structures, such as loops and function definitions, rather than braces as in some other languages like Java or JavaScript.

The colon : is used to start a new block of code, and then any lines that follow with an increased level of indentation are considered to be part of that block. The block continues until the indentation level is reduced.

Here is an example with an if statement and a loop:

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if x > 0:
    for i in range(x):
        print(i)

In this example, the : at the end of the if statement starts a new block of code, and the next two lines (with the for loop and the print statement) are indented to show that they are part of this block. The : at the end of the for statement also starts a new block of code, and the print statement is part of this inner block.

This design encourages writing code with clear and consistent indentation, which improves readability. However, it also means that indentation errors can cause bugs that might be difficult to track down.

title: Max Consecutive Ones excerpt: This covers the building block updating maximum on the fly. tags: update-maximum-inside-loop frequency-counter

Given a binary array nums, return the maximum number of consecutive 1’s in the array.

Example 1:
Input: nums = [1,1,0,1,1,1]
Output: 3
Explanation: The first two digits or the last three digits are consecutive 1s. The maximum number of consecutive 1s is 3.

Example 2:
Input: nums = [1,0,1,1,0,1]
Output: 2

Constraints

  • 1 <= nums.length <= 105
  • nums[i] is either 0 or 1.

Note:

  • The input array will only contain 0 and 1.
  • The length of input array is a positive integer and will not exceed 10,000

Questions

  • What is the starting point for the window?
  • How do you detect that a new window of 1s has started?
  • How do you detect the ending point for an existing window?
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# @param {Integer[]} nums
# @return {Integer}
def find_max_consecutive_ones(nums)
  count = 0
  result = 0
    
  for i in (0..nums.size-1)
    if nums[i] == 1
      count += 1
    else
      count = 0
    end
    result = [result, count].max
  end
    
  result
end

Building Blocks

  • Update Maximum Inside Loop
  • Frequency Counter

Complexity Analysis

Time Complexity: O(N), where N is the number of elements in the array. Space Complexity: O(1). We do not use any extra space.