75. Sort Colors

Problem

Tags: Array, Two Pointers, Sorting

Given an array nums 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.

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

You must solve this problem without using the library's sort function.

Example 1:

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

Example 2:

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

Constraints:

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

Follow up: Could you come up with a one-pass algorithm using only constant extra space?

Code

JS

// 75. Sort Colors (1/11/53841)
// Runtime: 72 ms (61.00%) Memory: 39.01 MB (94.75%) 

/**
 * @param {number[]} nums
 * @return {void} Do not return anything, modify nums in-place instead.
 */
function sortColors(nums) {
    const length = nums.length;
    let count = [0, 0, 0];
    for(let i = 0; i < length; i++) count[nums[i]]++;
    let idx = 0;
    for(let i = 0; i < 3; i++) 
        for(let j = 0; j < count[i]; j++) 
            nums[idx++] = i;
};