A powerful technique for solving array and string problems efficiently. Use two pointers moving from different positions to find optimal solutions.
// Two Sum - Sorted Array
function twoSum(nums, target) {
let left = 0, right = nums.length - 1;
while (left < right) {
const sum = nums[left] + nums[right];
if (sum === target) return [left, right];
else if (sum < target) left++;
else right--;
}
return [];
}
Practice Problems:
Container With Most Water
Valid Palindrome
Medium
Binary Search
Essential for searching in sorted arrays. Master the template and variants like finding first/last occurrence.
// Binary Search Template
function binarySearch(nums, target) {
let left = 0, right = nums.length - 1;
while (left <= right) {
const mid = Math.floor((left + right) / 2);
if (nums[mid] === target) return mid;
else if (nums[mid] < target) left = mid + 1;
else right = mid - 1;
}
return -1;
}
💡
Pro Tip: Always consider the time and space complexity of your solution. Interviewers love to see optimization thinking!
Data Structures
Easy
Arrays & Hash Maps
Foundation of most coding problems. Understand when to use arrays vs hash maps for optimal lookups.
// Hash Map for frequency counting
function charFrequency(str) {
const freq = {};
for (const char of str) {
freq[char] = (freq[char] || 0) + 1;
}
return freq;
}
Medium
Linked Lists
Master pointer manipulation, cycle detection, and reversal techniques.
// Reverse Linked List
function reverseList(head) {
let prev = null, curr = head;
while (curr) {
const next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
Hard
Trees & Graphs
Essential for system design and complex algorithmic problems. Practice DFS, BFS, and tree traversals.
// Binary Tree Inorder Traversal
function inorderTraversal(root) {
const result = [];
function dfs(node) {
if (!node) return;
dfs(node.left);
result.push(node.val);
dfs(node.right);
}
dfs(root);
return result;
}
System Design
Scalability Fundamentals
Learn to design systems that can handle millions of users. Focus on load balancing, caching, and database optimization.
Common System Design Questions:
Design a URL Shortener (like bit.ly)
Design a Chat Application
Design a Social Media Feed
Coding Tips
Problem-Solving Framework
Understand: Ask clarifying questions
Plan: Think through approach before coding
Code: Write clean, readable code
Test: Walk through examples
Optimize: Discuss improvements
🎯
Communication is Key: Think out loud during coding. Explain your approach, trade-offs, and decisions to the interviewer.
Behavioral Questions
STAR Method
Structure your answers using Situation, Task, Action, Result format for compelling storytelling.
Common Behavioral Questions:
"Tell me about a challenging project"
"Describe a time you disagreed with a team member"