Sorting an Array of 0s, 1s, and 2s Using Java

Sorting an Array of 0s, 1s, and 2s Using Java

Sorting an array that contains only 0s, 1s, and 2s is a common problem in programming. The task is to arrange the elements in ascending order without using any built in sorting function. A simple and efficient way to solve this problem is by using the Dutch National Flag algorithm. This approach helps to sort the array in a single pass using three pointers.

In this method, three variables are used, named low, mid, and high. The low pointer is used to place 0s at the beginning of the array, the mid pointer is used to check each element, and the high pointer is used to place 2s at the end. The process starts with all three pointers at their initial positions. While the mid pointer is less than or equal to high, the array is checked element by element. If the current element is 0, it is swapped with the element at the low position, and both low and mid are moved forward. If the element is 1, only the mid pointer is moved. If the element is 2, it is swapped with the element at the high position, and the high pointer is moved backward.

This process continues until all elements are checked. By the end, all 0s will be at the beginning, all 1s in the middle, and all 2s at the end. This method works efficiently because it requires only one traversal of the array. The time complexity is linear, and no extra space is required.

This problem helps in understanding pointer usage and efficient sorting techniques. It is an important concept for beginners and is often asked in exams and interviews.