Grokking the Coding Interview: Patterns for Coding Questions
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Solution: Dutch National Flag Problem
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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.

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