Selection sort is an algorithm where we keep finding the smallest element and then we order them in sequence. I dabble in C/C++, Java too. The reason for this is that Insertion Sort requires, on average, half as many comparisons. Selection sort is the in-place sorting algorithm, Why? Selection Sort Algorithm with Example is given. At every step, you have to find the minimum element and put it in the right place. However, with elements sorted in descending order, we only have half as many swap operations as elements! © 2020 – CSEstack.org. That is, no matter how many elements we sort – ten or ten million – we only ever need these five additional variables. In each loop cycle, the first element of the right part is initially assumed as the smallest element min; its position is stored in minPos. In the best case, it saves your program execution time. You can find the source code for the entire article series in my GitHub repository. It takes the complexity of O(n). This is not the case with sequential writes to arrays, as these are mostly done in the CPU cache. No extra space is required (in-place sorting), It has very high time complexity. The algorithm maintains two subarrays in a given array. You will find more sorting algorithms in this overview of all sorting algorithms and their characteristics in the first part of the article series. My focus is on optimizing complex algorithms and on advanced topics such as concurrency, the Java memory model, and garbage collection. The outer loop iterates over the elements to be sorted, and it ends after the second-last element. Selection sort Time Complexity. So no element is swapped. After the inner loop has been completed, the elements of positions i (beginning of the right part) and minPos are swapped (unless they are the same element). Note: For most efficient algorithm as per time complexity, you can use heap or merge sort. The time complexity measures the number of iterations required to sort the list. But to find out the smallest element, we need to iterate and check for all the elements in the array. That would not only go beyond the scope of this article, but of the entire blog. Here are the average values after 100 iterations (a small excerpt; the complete results can be found here): Here as a diagram with logarithmic x-axis: The chart shows very nicely that we have logarithmic growth, i.e., with every doubling of the number of elements, the number of assignments increases only by a constant value. I'm a freelance software developer with more than two decades of experience in scalable Java enterprise applications. Selection Sort has significantly fewer write operations, so Selection Sort can be faster when writing operations are expensive. The number of assignment operations for minPos and min is thus, figuratively speaking, about “a quarter of the square” – mathematically and precisely, it’s ¼ n² + n – 1. The inner loop then iterates from the second element of the right part to its end and reassigns min and minPos whenever an even smaller element is found. The inner loop (search for the smallest element) can be parallelized by dividing the array, searching for the smallest element in each sub-array in parallel, and merging the intermediate results. Within each iteration, you have to find out smallest element in the array. In the following steps, I show how to sort the array [6, 2, 4, 9, 3, 7] with Selection Sort: We divide the array into a left, sorted part and a right, unsorted part. An example can be constructed very simply. Required fields are marked *, Name *. If you look at steps 2, 3, 4 and 5 iterates ‘n’ number of times. With a linked list, cutting and pasting the element to be sorted could be done without any significant performance loss. Selection Sort is an easy-to-implement, and in its typical implementation unstable, sorting algorithm with an average, best-case, and worst-case time complexity of O(n²). All Rights Reserved. In total, there are 15 comparisons – regardless of whether the array is initially sorted or not. (O(n^2) in all three cases.) This program and algorithm sort the array in ascending order. Select the smallest element from the array. Here, all three complexity will be the same. Some of the simple and widely used algorithms are as follows. This webpage covers the space and time Big-O complexities of common algorithms used in Computer Science. To sort an array with Selection Sort, you must iterate through the array once for every value you have in the array. 1. If you want to sort the array in descending order, (step 2 in the algorithm) find the largest element rather than the smallest element. So the total complexity of the Selection sort algorithm is O(n)* O(n) i.e. We go to the next field, where we find an even smaller element in the 2. You find further information and options to switch off these cookies in our, SelectionSort class in the GitHub repository, overview of all sorting algorithms and their characteristics. The sorted part is empty at the beginning: We search for the smallest element in the right, unsorted part. This is all about Selection Sort in C with Explanation. Then you look for the next larger card and place it to the right of the smallest card, and so on until you finally pick up the largest card to the far right. Replace the smallest element with the array element placed at position ‘i’. We denote with n the number of elements, in our example n = 6. In the third step, only one element remains; this is automatically considered sorted. The list is divided into two partitions: The first list contains sorted items, while the second list contains unsorted items. If you liked the article, feel free to share it using one of the share buttons at the end. Time and Space Complexity. This is all about Selection Sort in C with Explanation. This will be the case if both loops iterate to a value that increases linearly with n. It is obviously the case with the outer loop: it counts up to n-1. The array NIT Trichy would have to find out the smallest card and inserted it in the program.! Sorted section finish executing relative to the array ascending order ascending order 3 4. Of its time complexity ( without complicated math ). points to the triangle of orange-blue. Behind the element to be sorted, and website in this article using examples and.! 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