Egbert Lin's Blog

204. Count Primes

Question:

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

Example:

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

203. Remove Linked List Elements

Question:

Remove all elements from a linked list of integers that have value val.

Example:

Input: 1->2->6->3->4->5->6, val = 6
Output: 1->2->3->4->5

202. Happy Number

Question:

Write an algorithm to determine if a number n is happy.

A happy number is a number defined by the following process:

• Starting with any positive integer, replace the number by the sum of the squares of its digits.
• Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
• Those numbers for which this process ends in 1 are happy.

Return true if n is a happy number, and false if not.

191. Number of 1 Bits

Question:

Write a function that takes an unsigned integer and returns the number of '1' bits it has (also known as the Hamming weight).

• Note that in some languages such as Java, there is no unsigned integer type. In this case, the input will be given as a signed integer type. It should not affect your implementation, as the integer's internal binary representation is the same, whether it is signed or unsigned.
• In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 3 above, the input represents the signed integer. -3 .

190. Reverse Bits

Question:

Reverse bits of a given 32 bits unsigned integer.

• Note that in some languages such as Java, there is no unsigned integer type. In this case, both input and output will be given as a signed integer type. They should not affect your implementation, as the integer's internal binary representation is the same, whether it is signed or unsigned.
• In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 2 above, the input represents the signed integer -3 and the output represents the signed integer -1073741825.

Basic programming - Exponential Search

Question:

Given a sorted array, and an element x to be searched, find position of x in the array.

Basic programming - Binary Search

Question:

Given a sorted array arr[] of n elements, write a function to search a given element x in arr[].

172. Factorial Trailing Zeroes

Question:

Given an integer n, return the number of trailing zeroes in n!.

Follow up: Could you write a solution that works in logarithmic time complexity?

Basic programming - Linear Search

Question:

Given an array arr[] of n elements, write a function to search a given element x in arr[].

171. Excel Sheet Column Number

Question:

Given a column title as appear in an Excel sheet, return its corresponding column number.

  A -> 1
  B -> 2
  C -> 3
  ...
  Z -> 26
  AA -> 27
  AB -> 28
  ...