sort-colors

Sort Colors

LeetCode #: 75

Difficulty: Medium

Topics: Array, Two Pointers, Sort.

Problem

Given an array with n objects colored red, white or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note: You are not suppose to use the library's sort function for this problem.

Example:

Input: [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

Follow up:

• A rather straight forward solution is a two-pass algorithm using counting sort.

  First, iterate the array counting number of 0's, 1's, and 2's, then overwrite array with total number of 0's, then 1's and followed by 2's.

• Could you come up with a one-pass algorithm using only constant space?

Solution Explanation

There are two solutions for this problem. Both has O(n) one-pass time complexity and O(1) space complexity.

1. Array manipulation approach which uses splice, unshift and push array methods. This approach performs faster on the LeetCode platform.

2. Pointers approach which uses multiple index pointers to perform array element swapping.