Grokking 75: Top Coding Interview Questions
Ask Author
Back to course home

0% completed

Dutch National Flag Problem (medium)
Table of Contents

Problem Statement

Examples

Example 2

Try it yourself

Problem Statement

Given an array containing 0s, 1s and 2s, sort the array in-place. You should treat numbers of the array as objects, hence, we can’t count 0s, 1s, and 2s to recreate the array.

The flag of the Netherlands consists of three colors: red, white and blue; and since our input array also consists of three different numbers that is why it is called Dutch National Flag problem.

Examples

Example 1

  • Input: arr = [1, 0, 2, 1, 0]
  • Output: [0, 0, 1, 1, 2]
  • Explanation:
    • All 0s are moved to the front, 1s in the middle, and 2s at the end.
    • The relative order within each group doesn't matter.

Example 2

  • Input: arr= [2, 2, 0, 1, 2, 0]
  • Output: [0, 0, 1, 2, 2, 2]
  • Explanation:
    • All 0s come first, followed by the 1, and then all 2s at the end.
    • Sorting is done in-place without using extra space or counting.

Constraints:

  • n == arr.length
  • 1 <= n <= 300
  • arr[i] is either 0, 1, or 2.

Try it yourself

Try solving this question here:

Python3
Python3
. . . .
Mark as Completed

Table of Contents

Problem Statement

Examples

Example 2

Try it yourself