Notes, summaries, assignments, exams, and problems for Computers

1. Anagram Detection: C++ String Comparison

This C++ program determines if two input strings are anagrams of each other. It achieves this by converting both strings to lowercase, sorting their characters alphabetically, and then comparing the sorted strings. If they are identical, the original strings are considered anagrams.

#include<bits/stdc++.h>
using namespace std;

int main(){
    string s2,s1;
    cin>>s1>>s2;
    transform(s1.begin(),s1.end(),s1.begin(),::tolower);
    transform(s2.begin(),s2.end(),s2.begin(),::tolower);
    sort(s1.begin(),s1.end());
    sort(s2.begin(),s2.end());
    cout<< (s2==s1);
}

2. Array Subarray: C++ Sliding Window Minimum

This C++ program attempts to find the maximum of minimums within... Continue reading "C++ & C Programming Solutions: Algorithms & Patterns" »

Longest Substring Without Repeating Characters

This problem involves finding the length of the longest substring in a given string that does not contain any repeating characters. A common approach uses a sliding window technique with a Set to efficiently track unique characters.

Strategy:

• Utilize a Set to store characters within the current window.
• Iterate through the string with a right pointer, adding characters to the Set.
• If a duplicate character is encountered, move the left pointer forward, removing characters from the Set, until the duplicate is no longer present.
• At each step, update the maximum length found.

Java Implementation Snippet

class Solution {
    public int findLongestSubstringWithoutRepeatingCharacter(String str) {
        Set&

Nmap Options

-PE: Quickly check if host is up.

-sn: Disable port scanning (host discovery).

-n: Disables DNS resolution (checks IP online without looking up hostnames).

-O: OS detection.

-A: OS detection, Version detection, Script scanning, traceroute.

-sV: Service detection (banner info, version).

-vV: Provides verbose output.

-sC: Scan with default scripts for additional info gathering.

--min-rate=5000: Ensures scan sends at least 5k packets per second.

nmap --script smb-enum-shares.nse -p 445 (ip): List shares and their properties.

To see scripts starting with X: ls /path/X

To execute script with script tracing: sudo nmap -script=smb-os-discovery -script-trace target_ip

To enumerate the SMB share files: sudo nmap -script=smb-enum-shares target_ip

Vulnerability... Continue reading "Nmap, Netcat, and Metasploit Commands Cheat Sheet" »

This document presents Java code snippets demonstrating two distinct functionalities: user name generation and management, and a car repair scheduling system. Each section includes method implementations with explanations of their purpose and logic.

User Name Management System

The UserName class is designed to generate and manage potential user names based on a user's first and last names. It also provides functionality to filter out names that are already in use.

UserName Class Constructor

This constructor initializes a UserName object, populating a list of possible user names. It assumes that firstName and lastName are valid strings containing only letters and have a length greater than zero.

import java.util.ArrayList;

public class UserName {

BPSK Signal Generation

This section demonstrates the generation of a Binary Phase Shift Keying (BPSK) signal using Python.

import numpy as np
import matplotlib.pyplot as plt

def bpsk_detect(modulated_signal, carrier):
    return np.sign(modulated_signal * carrier)

message_frequency = 10
carrier_frequency = 20
sampling_frequency = 30 * carrier_frequency
t = np.arange(0, 4/carrier_frequency, 1/sampling_frequency)
message = np.sign(np.cos(2 * np.pi * message_frequency * t) + np.random.normal(scale = 0.01, size = len(t)))
carrier = np.cos(2 * np.pi * sampling_frequency/carrier_frequency * t)
modulated_signal = carrier * message
detected_message = bpsk_detect(modulated_signal, carrier)

plt.figure(figsize=(12, 8))
plt.subplot(4, 1, 1)
plt.plot(t,

Core Concepts in Compiler Design

Compiler

Compiler: Translates entire source code to target code before execution. It requires a full parse and upfront error checking, then executes the generated target code.

Interpreter

Interpreter: Executes source code incrementally (line-by-line or statement-by-statement). It translates and executes on the fly, and may partially execute ill-formed programs until an error is encountered.

LVar vs. x86 Architecture

LVar: Features nested expressions, implicit control flow (represented by an Abstract Syntax Tree - AST), and an unlimited number of logical variables.

x86: Characterized by flat instructions, atomic operands (registers/memory), explicit control flow (jumps), and a limited set of registers. Compilation passes... Continue reading "Core Concepts in Compiler Design and Language Runtime" »

Digital Logic Circuits

Flip-Flops

Clocked RS Flip-Flop Drawbacks

Clocked RS flip-flops have some drawbacks, such as susceptibility to race conditions, where the output can become unpredictable if the inputs change too close to the clock edge. They also require careful handling of the inputs to avoid metastability issues, which can lead to incorrect output states. Additionally, they can have higher power consumption compared to other flip-flop types due to the need for a clock signal.

JK Flip-Flop Operation

Content about JK Flip-Flop operation, characteristic table, characteristics equation, circuit diagram, and timing diagram would be added here.

Magnitude Comparator

What is a Magnitude Comparator?

A magnitude comparator is a digital circuit that compares... Continue reading "Digital Logic Circuits: Flip-Flops, Comparators, Decoders, and Registers" »