Leetcode 75 Questions Flashcards

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Questions and Answers

What approach does 'Two Sum' use to check for the difference value?

Dynamic programming

Sorting the array

Brute force

Using a hash map (correct)

What is the primary strategy for solving 'Best Time to Buy and Sell Stock'?

Find local min and local max using a sliding window.

How does 'Contains Duplicate' check for duplicates in an array?

Using a hash set to get unique values.

What strategy is used in 'Product of Array Except Self'?

Make two passes through the array, first in-order and then in-reverse. Signup and view all the answers

What is the dynamic programming approach for 'Maximum Subarray'?

Compute the max sum for each prefix, ensuring the previous subarray is not negative. Signup and view all the answers

What is the dynamic programming technique used in 'Maximum Product Subarray'?

Compute max and max-abs-val for each prefix subarray. Signup and view all the answers

How do you identify the pivot in 'Find Minimum in Rotated Sorted Array'?

Check if half of the array is sorted. Signup and view all the answers

What is the main concept behind 'Search in Rotated Sorted Array'?

Identify if the target is in the range of the sorted portion, then search accordingly. Signup and view all the answers

How is the '3Sum' problem approached?

Sort the input and use two pointers to find pairs matching the sum with the first element. Signup and view all the answers

What technique is used in 'Container With Most Water'?

Use a shrinking window with pointers initially at the endpoints. Signup and view all the answers

What method is used to add two integers in 'Sum of Two Integers'?

Add bit by bit, considering carry. Signup and view all the answers

How do you determine the number of '1' bits in 'Number of 1 Bits'?

Use bit shift instead of modulo to determine the 1's place. Signup and view all the answers

What is the approach taken in 'Counting Bits'?

Identify a pattern by calculating results for powers of 2. Signup and view all the answers

What strategy is used in 'House Robber'?

For each number, calculate the maximum of the previous subarray or the current number plus the previous subarray excluding the last element. Signup and view all the answers

What is the key concept in 'House Robber II'?

Determine the maximum of the subarray excluding the first and last elements. Signup and view all the answers

What is the recursive strategy for 'Decode Ways'?

Evaluate if the current character can be decoded in one or two ways and use caching. Signup and view all the answers

How is 'Unique Paths' optimized?

Work backwards from the solution and only store the previous row. Signup and view all the answers

What visualization technique is applied in 'Jump Game'?

Visualize the recursive tree and use caching for O(n) time complexity. Signup and view all the answers

What is the method used in 'Clone Graph'?

Use recursive depth-first search with a hashmap for visited nodes. Signup and view all the answers

How is 'Course Schedule' approached?

Build an adjacency list and perform depth-first search to detect loops. Signup and view all the answers

What technique does 'Pacific Atlantic Water Flow' utilize?

Perform DFS on each cell to track which reaches the Pacific and Atlantic oceans. Signup and view all the answers

How is 'Number of Islands' solved?

Run DFS for each cell that is '1' and unvisited, marking contiguous '1's as visited. Signup and view all the answers

What is the approach for 'Longest Consecutive Sequence'?

Use a brute-force method with optimization through a hash set. Signup and view all the answers

What is the objective in 'Alien Dictionary'?

Create an adjacency list based on the order of characters in the words. Signup and view all the answers

Study Notes

Two Sum (Arrays)

Use a hash map for instant lookup of difference values.
Store the index of the last occurrence of each number to avoid reusing the same element.

Best Time to Buy and Sell Stock (Arrays)

Identify local minimum prices and local maximum prices.
Implement a sliding window approach to determine optimal buy/sell times.

Contains Duplicate (Arrays)

Utilize a hash set to filter and track unique values in the array.
Efficiently check for the existence of duplicates.

Product of Array Except Self (Arrays)

Perform two passes: first in normal order, second in reverse order.
Calculate the product of all elements except the current one during these passes.

Maximum Subarray (Arrays)

Employ dynamic programming with a focus on non-negative subarrays.
Maintain the maximum sum for each prefix of the array.

Maximum Product Subarray (Arrays)

Use dynamic programming to compute both maximum and maximum absolute value for each prefix subarray.

Find Minimum in Rotated Sorted Array (Arrays)

Determine if half of the array is sorted to locate the pivot point.
The array has at most two sorted subarrays.

Search in Rotated Sorted Array (Arrays)

Analyze whether the mid-point belongs to the left or right sorted half.
If the target lies within a sorted half, search there; otherwise, search the other half.

3Sum (Arrays)

Sort the input array and iterate for each first element.
Use the two-pointer technique to find pairs that sum to the negative of the first element while skipping duplicates.

Container With Most Water (Arrays)

Implement a shrinking window approach with left and right pointers at the endpoints.
Move the pointer pointing to the shorter height inward to maximize area.

Sum of Two Integers (Binary)

Perform bit-wise addition, incorporating carry values from previous calculations.
If a carry remains after processing all bits, add that as well.

Number of 1 Bits (Binary)

Avoid expensive modulo and division operations by utilizing bit shifts and bitwise operations.
Use & with 1 to ascertain the least significant bit.

Counting Bits (Binary)

Analyze the output for numbers up to 16 to identify patterns in bit counting.
Use results from previous numbers to find current counts iteratively.

House Robber (Dynamic Programming)

Calculate the maximum profit by deciding between including or excluding the previous house.
Store the results of previous calculations for efficiency.

House Robber II (Dynamic Programming)

Analyze subarrays with either the first or last house excluded.
Determine which of the two ends can provide maximum profit when included.

Decode Ways (Dynamic Programming)

Assess whether each character can be decoded in one or two ways, considering edge cases.
Transition from recursion with caching to an iterative dynamic programming approach.

Unique Paths (Dynamic Programming)

Work backwards from the end solution to count unique paths.
Optimize storage usage by holding only the previous row of the grid.

Jump Game (Dynamic Programming)

Visualize recursive solutions and apply caching for time complexity reduction.
Use backward iteration to determine if any position can reach the end efficiently.

Clone Graph (Graph)

Use recursive depth-first search (DFS) to traverse each node.
Maintain a hashmap to keep track of visited nodes.

Course Schedule (Graph)

Build an adjacency list representing connections between courses.
Implement DFS to detect cycles indicating course dependencies.

Pacific Atlantic Water Flow (Graph)

Use DFS to explore each cell in the grid and track cells accessible to both oceans.
Identify overlaps where certain cells can drain to both Pacific and Atlantic.

Number of Islands (Graph)

Traverse each cell, initiating DFS when encountering an unvisited land cell.
Increment the island count for each new contiguous land mass discovered.

Longest Consecutive Sequence (Graph)

Start with a brute-force solution and optimize by using a hash set for fast lookups.
For each number, check for the longest sequence of consecutive integers.

Alien Dictionary (Leetcode Premium) (Graph)

Analyze the order of characters in given words to establish relationships.
Construct an adjacency list representing the unique characters and their order based on differences from adjacent words.

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Description

This quiz features flashcards centered on Leetcode's 75 essential coding interview questions. Each card provides key concepts and strategies to tackle common programming challenges, focusing on arrays and data structures. Ideal for preparing for coding interviews and enhancing problem-solving skills.