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Today’s question from Daily leetcode challenge — February edition. This question has been asked in Google interviews. Let us look into the problem statement.

946. Validate Stack Sequences

Given two sequences pushed and popped with distinct values, return true if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.

Example 1:

Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
Output: true
Explanation: We might do the following sequence:
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1


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Today’s question from Daily leetcode challenge — February edition. Let us look into the problem statement.

581. Shortest Unsorted Continuous Subarray

Given an integer array nums, you need to find one continuous subarray that if you only sort this subarray in ascending order, then the whole array will be sorted in ascending order.

Return the shortest such subarray and output its length.

Example 1:

Input: nums = [2,6,4,8,10,9,15]
Output: 5
Explanation: You need to sort [6, 4, 8, 10, 9] in ascending order to make the whole array sorted in ascending order.

Example 2:

Input: nums = [1,2,3,4]
Output: 0


Day 83

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Today’s question is from Leetcode’s daily coding challenge February edition. Let us look into the problem statement.

991. Broken Calculator

On a broken calculator that has a number showing on its display, we can perform two operations:

  • Double: Multiply the number on the display by 2, or;
  • Decrement: Subtract 1 from the number on the display.

Initially, the calculator is displaying the number X.

Return the minimum number of operations needed to display the number Y.

Example 1:

Input: X = 2, Y = 3
Output: 2
Explanation: Use double operation and then decrement operation {2 -> 4 -> 3}.


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Today’s question is a SQL question. Let us look into the problem statement.

177. Nth Highest Salary

Write a SQL query to get the nth highest salary from the Employee table.

+----+--------+
| Id | Salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+

For example, given the above Employee table, the nth highest salary where n = 2 is 200. If there is no nth highest salary, then the query should return null.

+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200 |
+------------------------+

A few days back, we found the…


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Today’s question is a medium-tagged question on leetcode. The question is taken from the daily coding challenge February edition. Let us look into the problem statement.

277. Find the Celebrity

Suppose you are at a party with n people (labeled from 0 to n - 1), and among them, there may exist one celebrity. The definition of a celebrity is that all the other n - 1 people know him/her, but he/she does not know any of them.

Now you want to find out who the celebrity is or verify that there is not one. The only thing you are…


Day 80

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Today’s question is a Leetcode medium-tagged question. Let us look into the problem statement.

48. Rotate Image

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:


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Today’s question is based on SQL. A very easy question. Let us look into the problem statement.

175. Combine Two Tables

Table: Person

+-------------+---------+
| Column Name | Type |
+-------------+---------+
| PersonId | int |
| FirstName | varchar |
| LastName | varchar |
+-------------+---------+
PersonId is the primary key column for this table.

Table: Address

+-------------+---------+
| Column Name | Type |
+-------------+---------+
| AddressId | int |
| PersonId | int |
| City | varchar |
| State | varchar |
+-------------+---------+
AddressId is the primary key column for this table.

Write a SQL query…


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Today’s question is an easy tagged question from Leetcode. Let us look into the problem statement.

204. Count Primes

Count the number of prime numbers less than a non-negative number, n.

Example 1:

Input: n = 10
Output: 4
Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.

Example 2:

Input: n = 0
Output: 0

Example 3:

Input: n = 1
Output: 0

Constraints:

  • 0 <= n <= 5 * 106

One of the easiest ways to solve this problem is by checking if each number that is lesser than n is prime or not.

How…


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Today’s question is from Leetcode’s daily coding challenge February edition. It is a medium-tagged question on Leetcode. Let us look into the problem statement.

582. Kill Process

Given n processes, each process has a unique PID (process id) and its PPID (parent process id).

Each process only has one parent process, but may have one or more children processes. This is just like a tree structure. Only one process has PPID that is 0, which means this process has no parent process. All the PIDs will be distinct positive integers.

We use two lists of integers to represent a list…


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Today’s question is from leetcode’s daily coding challenge. This question is frequently asked in Facebook interviews. Let us look into the problem statement.

785. Is Graph Bipartite?

There is an undirected graph with n nodes, where each node is numbered between 0 and n - 1. You are given a 2D array graph, where graph[u] is an array of nodes that node u is adjacent to. More formally, for each v in graph[u], there is an undirected edge between node u and node v. The graph has the following properties:

  • There are no self-edges (graph[u] does not contain u).
  • There…

Annamariya Tharayil

Software Engineer. Find me @ www.linkedin.com/in/annamariya-jt

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