Selection sort code added

Author: me-shaon

Sorting/Selection Sort/README.md

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+# Selection Sort
+
+**Selection sort** is one of the simplest sorting algorithm.
+It works by selecting the smallest (or largest, if you want to sort from big to small) element of the array and placing it at the head of the array. Then the process is repeated for the remainder of the array; the next largest element is selected and put into the next slot, and so on down the line.
+
+![Selection Sort](selection_sort.jpg)
+
+Selection sort algorithm starts by compairing first two elements of an array and swapping if necessary, i.e., if you want to sort the elements of array in ascending order and if the first element is greater than second then, you need to swap the elements but, if the first element is smaller than second, leave the elements as it is. Then, again first element and third element are compared and swapped if necessary. This process goes on until first and last element of an array is compared. This completes the first step of selection sort.
+
+If there are n elements to be sorted then, the process mentioned above should be repeated n-1 times to get required result.
+
+#####A visualization on Selection Sort
+![Selection sort demonstration](https://upload.wikimedia.org/wikipedia/commons/9/94/Selection-Sort-Animation.gif)
+
+*Selection sort animation. Red is current min. Yellow is sorted list. Blue is current item.*
+
+####Complexity Analysis
+- Worst Case - O(n<sup>2</sup>)
+- Average Case - O(n<sup>2</sup>)
+- Best Case - O(n<sup>2</sup>)
+
+### More on this topic
+- https://en.wikipedia.org/wiki/Selection_sort
+- http://quiz.geeksforgeeks.org/selection-sort/
+- https://www.topcoder.com/community/data-science/data-science-tutorials/sorting/

Sorting/Selection Sort/selection-sort.js

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+//Simple Selection Sort implementation
+function selectionSort(arr){
+    var len = arr.length;
+
+    /* advance the position through the entire array */
+    /*   (could do i < n-1 because single element is also min element) */
+    for(var i=0; i<len-1; i++){
+        // find the min element in the unsorted a[i .. n-1]
+
+        var currentMin = i; // assume the min is the first element
+        // test against elements after i to find the smallest
+        for (var j=i+1; j<len; j++)
+        {
+            // if this element is less, then it is the new minimum
+            if (arr[j] < arr[currentMin]) //To sort in decreasing order just change the comparison operator to '>'
+                currentMin = j; // found new minimum; remember its index
+        }
+
+        if(currentMin != i) //if the current_Min is equal to i, then it is in right position already
+        {
+            //Swap the values
+            tmp = arr[i];
+            arr[i] = arr[currentMin];
+            arr[currentMin] = tmp;
+        }
+    }
+
+    return arr;
+}
+
+/******************* Testing Selection sort algorithm *********************/
+
+/**
+ * Returns a random integer between min (inclusive) and max (inclusive)
+ * Using Math.round() will give you a non-uniform distribution!
+ */
+function getRandomInt(min, max) {
+    return Math.floor(Math.random() * (max - min + 1)) + min;
+}
+
+var arr = [];
+
+for(var i=0;i<10;i++){ //initialize a random integer unsorted array
+    arr.push(getRandomInt(1, 100));
+}
+
+console.log("Unsorted array: ");
+console.log(arr); //printing unsorted array
+
+arr = selectionSort(arr);
+console.log("Sorted array: ");
+console.log(arr); //printing sorted array