What is SQL injection and how to prevent it in Java?

In this post, we will learn about common coding mistakes in Java, which lead to a vulnerable application. Also, we are going to learn to avoid SQLi.

What is SQL injection?

SQLi or SQL injection is an attack where a hacker manages to inject unauthorized SQL query language code into an application. Due to this, the attacker manages to change the behavior of a legitimate query before it hits the database.

#LeetCode: Rotting Oranges

Also Check: August LeetCoding Challenge (2020)

In a given grid, each cell can have one of three values:

the value 0 representing an empty cell;
the value 1 representing a fresh orange;
the value 2 representing a rotten orange.
Every minute, any fresh orange that is adjacent (4-directionally) to a rotten orange becomes rotten.

Return the minimum number of minutes that must elapse until no cell has a fresh orange.  If this is impossible, return -1 instead.

#LeetCode: Path Sum III

Also Check: August LeetCoding Challenge (2020)

You are given a binary tree in which each node contains an integer value.

Find the number of paths that sum to a given value.

The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).

#LeetCode: Add and Search Word - Data structure design

Design a data structure that supports the following two operations:

• void addWord(word)
• bool search(word)

search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.

#LeetCode: Power of Four

Also Check: August LeetCoding Challenge (2020)

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example 1:
Input: 16
Output: true

#LeetCode: Valid Palindrome

Also Check: August LeetCoding Challenge (2020)

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:
Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:
Input: "race a car"
Output: false

#LeetCode: Design HashSet

Also Check: August LeetCoding Challenge (2020)

Design a HashSet without using any built-in hash table libraries.

To be specific, your design should include these functions:

• add(value): Insert a value into the HashSet. 
• contains(value) : Return whether the value exists in the HashSet or not.
• remove(value): Remove a value in the HashSet. If the value does not exist in the HashSet, do nothing.

#LeetCode : Detect Capital

Also Check: August LeetCoding Challenge (2020)

Given a word, you need to judge whether the usage of capitals in it is right or not.

We define the usage of capitals in a word to be right when one of the following cases holds:

• All letters in this word are capitals, like "USA".
• All letters in this word are not capitals, like "leetcode".
• Only the first letter in this word is capital, like "Google".
• Otherwise, we define that this word doesn't use capitals in a right way.

How to implement Snakes and Ladders using Java?

ALSO CHECK: Algorithms and System Design Interview Questions

Let's create a SnakeNLadder.java class. Define constant WINPOINT with value 100. Each player has to start the journey from 0, roll the dice and try to reach WINPOINT.

Sapient Interview Questions

ALSO CHECK: Interview Questions and Answers of All IT Companies

First Round: Live coding test

1). Asked me to create an employee class with a couple of fields like employee id, date of joining, salary age.

#LeetCode : Power Of Two

Also Check: June LeetCoding Challenge (2020)

Given an integer, write a function to determine if it is a power of two.

Example 1:

Input: 1
Output: true 
Explanation: 20 = 1

#LeetCode : Coin Change 2

Also Check: June LeetCoding Challenge (2020)

You are given coins of different denominations and a total amount of money. Write a function to compute the number of combinations that make up that amount. You may assume that you have infinite number of each kind of coin.

Example 1:
Input: amount = 5, coins = [1, 2, 5]
Output: 4
Explanation: there are four ways to make up the amount:
5=5
5=2+2+1
5=2+1+1+1
5=1+1+1+1+1

#LeetCode :Queue Reconstruction by Height

Also Check: June LeetCoding Challenge (2020)

Suppose you have a random list of people standing in a queue. Each person is described by a pair of integers (h, k), where h is the height of the person and k is the number of people in front of this person who have a height greater than or equal to h. Write an algorithm to reconstruct the queue.

Note:
The number of people is less than 1,100.

Example
Input:[[7,0], [4,4], [7,1], [5,0], [6,1], [5,2]]
Output:[[5,0], [7,0], [5,2], [6,1], [4,4], [7,1]]

#LeetCode : Reverse String

Also Check: June LeetCoding Challenge (2020)

Write a function that reverses a string. The input string is given as an array of characters char[].

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

You may assume all the characters consist of printable ascii characters.

#LeetCode : Two City Scheduling

Also Check: June LeetCoding Challenge (2020)

There are 2N people a company is planning to interview. The cost of flying the i-th person to city A is costs[i][0], and the cost of flying the i-th person to city B is costs[i][1].

Return the minimum cost to fly every person to a city such that exactly N people arrive in each city.

Example 1:
Input: [[10,20],[30,200],[400,50],[30,20]]
Output: 110
Explanation:
The first person goes to city A for a cost of 10.
The second person goes to city A for a cost of 30.
The third person goes to city B for a cost of 50.
The fourth person goes to city B for a cost of 20.

The total minimum cost is 10 + 30 + 50 + 20 = 110 to have half the people interviewing in each city.

#LeetCode Delete Node in a Linked List

Also Check: June LeetCoding Challenge (2020)

Write a function to delete a node (except the tail) in a singly linked list, given only access to that node.

Example 1:
Input: head = [4,5,1,9], node = 5
Output: [4,1,9]
Explanation: You are given the second node with value 5, the linked list should become 4 -> 1 -> 9 after calling your function.

#LeetCode: Invert Binary Tree

Also Check: June LeetCoding Challenge (2020)

Invert the given Binary tree

#LeetCode: Edit Distance

Also Check: Solutions Of May LeetCoding Challenge (2020)

Given two words word1 and word2, find the minimum number of operations required to convert word1 to word2.

You have the following 3 operations permitted on a word:

• Insert a character
• Delete a character
• Replace a character

#LeetCode: K Closest Points to Origin

Also Check: Solutions Of May LeetCoding Challenge (2020)

We have a list of points on the plane.  Find the K closest points to the origin (0, 0).(Here, the distance between two points on a plane is the Euclidean distance.)

You may return the answer in any order.  The answer is guaranteed to be unique (except for the order that it is in.)

#LeetCode: Course Schedule

Also Check: Solutions Of May LeetCoding Challenge (2020)

There are a total of numCourses courses you have to take, labeled from 0 to numCourses-1.

Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1]

Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses?

Example 1:
Input: numCourses = 2, prerequisites = [[1,0]]
Output: true
Explanation: There are a total of 2 courses to take.
             To take course 1 you should have finished course 0. So it is possible.

Example 2:
Input: numCourses = 2, prerequisites = [[1,0],[0,1]]
Output: false
Explanation: There are a total of 2 courses to take.
             To take course 1 you should have finished course 0, and to take course 0 you should
             also have finished course 1. So it is impossible.

Constraints:
The input prerequisites is a graph represented by a list of edges, not adjacency matrices. Read more about how a graph is represented.
You may assume that there are no duplicate edges in the input prerequisites.
1 <= numCourses <= 10^5

GIT URL: Java Solution of Leet Code's Course Schedule problem

Java Solution 1

ALSO CHECK: Other LeetCode Solutions in Java

-K Himaanshu Shuklaa.