Sort Colors

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.

LeetCode Problem - 75

class Solution {
    public void sortColors(int[] nums) {
        // Create a HashMap to count occurrences of each color (0, 1, or 2)
        Map<Integer, Integer> countMap = new HashMap<>();

        // Count occurrences of each color in nums array
        for (int num : nums) {
            countMap.put(num, countMap.getOrDefault(num, 0) + 1);
        }

        int idx = 0; // Index to update nums array

        // Iterate through the HashMap and reconstruct nums array in sorted order
        for (int color : countMap.keySet()) {
            int count = countMap.get(color);

            // Place each color in nums array according to its count
            for (int i = 0; i < count; i++) {
                nums[idx++] = color;
            }
        }
    }
}