How do you solve Number of Senior Citizens on LeetCode?

Number of Senior Citizens (LeetCode #2678) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: Extracting age from a fixed position in a string is a common pattern.

What is the brute force solution for Number of Senior Citizens?

The brute force approach for Number of Senior Citizens is Brute Force, with O(n) time complexity and O(1) space complexity. The brute force approach involves checking each passenger's age by extracting the relevant characters from their details string and counting how many are over 60. This is straightforward but not the most efficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Number of Senior Citizens?

Number of Senior Citizens uses the following concepts: Array, String. The recommended patterns to study are: Array, String Manipulation.

What are the interview tips for Number of Senior Citizens?

Always clarify the input format and constraints. Think about edge cases, such as the minimum and maximum values. Practice explaining your thought process as you code.

What are common mistakes when solving Number of Senior Citizens?

Not correctly converting characters to integers. Overcomplicating the logic instead of keeping it simple.

#2678

Number of Senior Citizens

Easy

ArrayStringArrayString Manipulation

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n)	O(n)
Space	O(1)	O(1)

💡

Intuition

Time O(n)Space O(1)

The optimal solution is similar to the brute force approach but focuses on efficiency by directly extracting and calculating the age in a single pass through the array, maintaining the same time complexity but ensuring clarity.

⚙️

Algorithm

6 steps

1Step 1: Initialize a counter to zero.
2Step 2: Loop through each passenger's details in the array.
3Step 3: For each passenger, extract the age from the string using the characters at index 11 and 12.
4Step 4: Convert the extracted characters to an integer to get the age.
5Step 5: If the age is greater than 60, increment the counter.
6Step 6: Return the counter.

solution.py7 lines

1def countSeniorCitizens(details):
2    count = 0
3    for detail in details:
4        age = int(detail[11]) * 10 + int(detail[12])
5        if age > 60:
6            count += 1
7    return count

ℹ

Complexity note: The time complexity remains O(n) as we traverse the list once. The space complexity is O(1) since we only use a single counter variable.

1Extracting age from a fixed position in a string is a common pattern.
2Understanding how to convert characters to integers is crucial.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.