Sort Characters by Frequency

In this tutorial, I am going to discuss a very interesting problem sort characters by frequency.

Given a string, write a method to sort it in decreasing order based on the frequency of characters.

For example:

Example 1

Input : “teee”

Output: “eeet”

Example 2:

  Input: “dddbbb”

Output: “dddbbb”   or “bbbddd” (Both d and b appear 3 times so any of the above output are valid)

  Example 3:

  Input:  “Eett”

Output: “ttEe” or “tteE”  (Both e and E are two different characters so the output should not be “Eett”)

Find Longest Common Prefix in an Array of Strings

How to find longest common prefix in an array of strings.

Given an array of strings, write a method to find the longest common prefix string. If no common prefix is found, return an empty string ” “.

For example:

Example 1:

Input: [“cat”,”cable”,”camera”]
Output: “ca”

The longest common prefix is ca.

Example 2:

Input: [“rat”,”dog”,”elephant”]
Output: “”

No common prefix is found.