Summary Ranges

The problem asks to generate the smallest sorted list of ranges that cover all the numbers in the array exactly. Here’s how we can approach this:

  1. Initialize an empty result list.
  2. Iterate through the array, checking for consecutive numbers.
  3. If consecutive numbers are found, record the start and end of the range.
  4. Add the range to the result list in the desired format.

Below is the code:

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class Solution:
    def summaryRanges(self, nums: List[int]) -> List[str]:
        if not nums:
            return []

        result = []
        start = end = nums[0]

        for i in range(1, len(nums)):
            if nums[i] == end + 1:
                end = nums[i]
            else:
                if start == end:
                    result.append(str(start))
                else:
                    result.append(str(start) + "->" + str(end))
                start = end = nums[i]

        # Handle the last range
        if start == end:
            result.append(str(start))
        else:
            result.append(str(start) + "->" + str(end))

        return result

This code checks for consecutive numbers and constructs the ranges accordingly, making sure to handle the case when a range consists of only a single number. It returns the desired list of ranges for the given sorted unique integer array nums.

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class Solution:
	def summaryRanges(self, nums: List[int]) -> List[str]:
		result = []
		start , end = 0 , 0

		while start < len(nums) and end < len(nums):
			if (end + 1) < len(nums) and nums[end] + 1 == nums[end + 1]:
				end = end + 1
			else:
				if nums[start] == nums[end]:
					result.append(str(nums[start]))
					start = start + 1
					end = end + 1
				else:
					result.append(str(nums[start]) + '->' + str(nums[end]))
					end = end + 1
					start = end

		return result

Problem Classification

  1. Array Manipulation: The problem involves dealing with an array of integers and performing operations on it.

  2. Range Extraction: The primary task is to identify and extract the ranges of consecutive numbers.

  3. Formatting and Representation: The ranges identified need to be represented and formatted in a specific string format.

  4. Sequential Data Processing: The problem involves a sequential scanning process of the given data (array).

Language Agnostic Coding Drills

Here’s how you can break down the concepts in this problem:

  1. Arrays/Lists: Understanding how to iterate through a list or array, the concept of index, and using array length.

  2. Loops and Conditions: Understand how to use while loops and nested if-else conditions.

  3. String Manipulation: Understand how to convert an integer to a string and how to concatenate strings.

  4. Working with multiple variables and pointers: This problem requires keeping track of two pointers (start and end) simultaneously.

Now, let’s break down the problem-solving approach:

  1. Initialize variables: Start by initializing two pointers at the beginning of the list, start and end, along with an empty result list.

  2. Iterate over the list: Start a while loop which continues till both start and end are less than the length of the input list.

  3. Find a range: Inside the loop, check if end + 1 is still within the array bounds and if the next number is a continuation of the current sequence (nums[end] + 1 == nums[end + 1]). If so, increment end. This will extend the current range.

  4. Handle end of range or sequence: If the next number isn’t a continuation of the current sequence, we’ve found the end of a range. Check if start and end are pointing to the same number. If so, append it to the result as a string. If not, append the range (from start to end) as a string to the result.

  5. Move to next range: After appending to the result, move the start and end pointers appropriately to start tracking the next range.

  6. Final result: Return the result list which contains all the ranges in string format.

The problem can then be solved by integrating these concepts and following the problem-solving approach.

Targeted Drills in Python

  1. Working with Arrays/Lists:
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# Create a list of integers
nums = [0, 1, 2, 4, 5, 7, 8, 9]

# Print each element of the list
for num in nums:
    print(num)

# Print the length of the list
print(len(nums))

# Print an element at a specific index
print(nums[3])
  1. Loops and Conditions:
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# Create a counter
counter = 0

# Use a while loop to increment the counter until it reaches a certain number
while counter < 10:
    print(counter)
    counter += 1
  1. String Manipulation:
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# Convert an integer to a string
num = 5
str_num = str(num)
print(str_num)

# Concatenate two strings
str1 = "Hello"
str2 = "World"
concatenated = str1 + " " + str2
print(concatenated)
  1. Working with multiple variables and pointers:
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# Initialize two pointers
start, end = 0, 0

# Simulate a situation where start and end move along an array
nums = [0, 1, 2, 4, 5, 7, 8, 9]

while start < len(nums) and end < len(nums):
    print(f"Start: {start}, End: {end}")

    # Move the end pointer if the next element is a continuation of the sequence
    if (end + 1) < len(nums) and nums[end] + 1 == nums[end + 1]:
        end += 1
    else:
        print(f"Range: {start} -> {end}")
        start = end + 1
        end = start

The final solution can then be created by integrating all these concepts:

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class Solution:
    def summaryRanges(self, nums):
        start, end = 0, 0
        result = []

        while start < len(nums) and end < len(nums):
            if (end + 1) < len(nums) and nums[end] + 1 == nums[end + 1]:
                end += 1
            else:
                if start == end:
                    result.append(str(nums[start]))
                else:
                    result.append(str(nums[start]) + '->' + str(nums[end]))

                start = end + 1
                end = start

        return result

This code will correctly identify and format all consecutive ranges in the input array.