Code Snippets

// Binary Search implementation in JavaScript
function binarySearch(arr, target) {
  let left = 0;
  let right = arr.length - 1;
  
  while (left <= right) {
    const mid = Math.floor((left + right) / 2);
    
    if (arr[mid] === target) {
      return mid; // Target found
    } else if (arr[mid] < target) {
      left = mid + 1; // Search in the right half
    } else {
      right = mid - 1; // Search in the left half
    }
  }
  
  return -1; // Target not found
}

// Example usage
const sortedArray = [1, 3, 5, 7, 9, 11, 13, 15, 17];
const targetValue = 7;
const result = binarySearch(sortedArray, targetValue);

console.log(`Found ${targetValue} at index: ${result}`);

# Merge Sort implementation in Python
def merge_sort(arr):
    if len(arr) <= 1:
        return arr
    
    # Divide the array into two halves
    mid = len(arr) // 2
    left_half = arr[:mid]
    right_half = arr[mid:]
    
    # Recursively sort both halves
    left_half = merge_sort(left_half)
    right_half = merge_sort(right_half)
    
    # Merge the sorted halves
    return merge(left_half, right_half)

def merge(left, right):
    result = []
    i = j = 0
    
    # Compare elements from both arrays and add the smaller one to the result
    while i < len(left) and j < len(right):
        if left[i] <= right[j]:
            result.append(left[i])
            i += 1
        else:
            result.append(right[j])
            j += 1
    
    # Add remaining elements
    result.extend(left[i:])
    result.extend(right[j:])
    
    return result

# Example usage
unsorted_array = [38, 27, 43, 3, 9, 82, 10]
sorted_array = merge_sort(unsorted_array)
print(f"Sorted array: {sorted_array}")

// useLocalStorage.ts - Custom React hook for managing local storage
import { useState, useEffect } from 'react';

function useLocalStorage<T>(key: string, initialValue: T): [T, (value: T) => void] {
  // Get stored value from localStorage or use initialValue
  const readValue = (): T => {
    if (typeof window === 'undefined') {
      return initialValue;
    }

    try {
      const item = window.localStorage.getItem(key);
      return item ? JSON.parse(item) : initialValue;
    } catch (error) {
      console.warn(`Error reading localStorage key "${key}":`, error);
      return initialValue;
    }
  };

  // State to store our value
  const [storedValue, setStoredValue] = useState<T>(readValue);

  // Return a wrapped version of useState's setter function that
  // persists the new value to localStorage
  const setValue = (value: T) => {
    try {
      // Allow value to be a function so we have the same API as useState
      const valueToStore = value instanceof Function ? value(storedValue) : value;
      
      // Save state
      setStoredValue(valueToStore);
      
      // Save to localStorage
      if (typeof window !== 'undefined') {
        window.localStorage.setItem(key, JSON.stringify(valueToStore));
      }
    } catch (error) {
      console.warn(`Error setting localStorage key "${key}":`, error);
    }
  };

  useEffect(() => {
    setStoredValue(readValue());
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [key]);

  return [storedValue, setValue];
}

export default useLocalStorage;

// Example usage:
// const [theme, setTheme] = useLocalStorage('theme', 'dark');

// Express.js API endpoint for user authentication
const express = require('express');
const bcrypt = require('bcrypt');
const jwt = require('jsonwebtoken');
const User = require('../models/User');

const router = express.Router();

// User login endpoint
router.post('/login', async (req, res) => {
  try {
    const { email, password } = req.body;

    // Validate input
    if (!email || !password) {
      return res.status(400).json({ message: 'Email and password are required' });
    }

    // Find user by email
    const user = await User.findOne({ email });
    if (!user) {
      return res.status(401).json({ message: 'Invalid credentials' });
    }

    // Check password
    const isPasswordValid = await bcrypt.compare(password, user.password);
    if (!isPasswordValid) {
      return res.status(401).json({ message: 'Invalid credentials' });
    }

    // Generate JWT token
    const token = jwt.sign(
      { userId: user._id, email: user.email },
      process.env.JWT_SECRET,
      { expiresIn: '1h' }
    );

    // Send response
    res.status(200).json({
      message: 'Login successful',
      token,
      user: {
        id: user._id,
        name: user.name,
        email: user.email
      }
    });
  } catch (error) {
    console.error('Login error:', error);
    res.status(500).json({ message: 'Server error' });
  }
});

module.exports = router;