Category: Recursion

Quicksort

technologeo

Programming Language:

Javascript (JS)

Solution:

// This function partitions given array and returns 
// the index of the pivot.
//var partition=function(array, p, r){
// This code has been purposefully obfuscated,
// as you will implement it yourself in next challenge
//    var e=array,t=p,n=r;var r=function(e,t,n){var r=e[t];e[t]=e[n];e[n]=r;};var i=t;for(var s=t;s<n;s++){if(e[s]<=e[n]){r(e,s,i);//i++;}}r(e,n,i);return i;
//};

// Swaps two items in an array, changing the original array
var swap = function(array, firstIndex, secondIndex) {
    var temp = array[firstIndex];
    array[firstIndex] = array[secondIndex];
    array[secondIndex] = temp;
};

// This function partitions given array and returns 
// the index of the pivot.
var partition = function(array, p, r) {
    // Compare array[j] with array[r], for j = p, p+1,...r-1
    var q = p;

    // maintaining that:
    // array[p..q-1] are values known to be <= to array[r]
    // array[q..j-1] are values known to be > array[r]
    // array[j..r-1] haven't been compared with array[r]
    // If array[j] > array[r], just increment j.
    // If array[j] <= array[r], swap array[j] with array[q],
    // increment q, and increment j. 
    for (var j = p; j < r; j++) {
        if (array[j] <= array[r]) {
            swap(array, j, q);
            q++;
        }
    }
    // Once all elements in array[p..r-1]
    //  have been compared with array[r],
    //  swap array[r] with array[q], and return q.
    swap(array, r, q);
    return q;
};

var array = [9, 7, 5, 11, 12, 2, 14, 3, 10, 4, 6];
var q = partition(array, 0, array.length-1);
println("Array after partitioning: " + array);
Program.assertEqual(q, 4);
Program.assertEqual(array, [5, 2, 3, 4, 6, 7, 14, 9, 10, 11, 12]);

var array = [-9, 7, 5, 11, 12, 2, 0, 3, 10, 4, -6];
var q = partition(array, 0, array.length-1);
println("Array after partitioning: " + array);
Program.assertEqual(q, 1);
Program.assertEqual(array, [-9, -6, 5, 11, 12, 2, 0, 3, 10, 4, 7]);

var quickSort = function(array, p, r) {
    if(p < r) {
        var pivotIndex = partition(array, p, r);
        quickSort(array, p, pivotIndex - 1);
        quickSort(array, pivotIndex + 1, r);
    }
};

var array = [9, 7, 5, 11, 12, 2, 14, 3, 10, 6];
quickSort(array, 0, array.length-1);
println("Array after sorting: " + array);
Program.assertEqual(array, [2,3,5,6,7,9,10,11,12,14]);

var array = [-9, 75, 54, 1, 12, 2, 18, 3, 0, -6];
quickSort(array, 0, array.length-1);
println("Array after sorting: " + array);
Program.assertEqual(array, [-9, -6, 0, 1, 2, 3, 12, 18, 54, 75]);

Sierpinski’s Gasket

technologeo

HTML 5/JS (Javascript)

<canvas id="sierpinski_canvas" width="750" height="750" style="border:1px solid #888;"></canvas>

<script>
var canvas = document.getElementById("sierpinski_canvas");
var canvasInfo = document.getElementById("sierpinski_canvas").getBoundingClientRect();
var canvasWidth = canvasInfo.width;
var canvasHeight = canvasInfo.height;
var ctx = canvas.getContext("2d");
var rectDim = 750;
var rectMinSize = 7;

function drawGasket(x, y, rectDim) {
    if (rectDim <= rectMinSize) {
            var randomColor = Math.floor(Math.random()*16777215).toString(16);
            ctx.fillStyle = "#" + randomColor;
	    ctx.fillRect(x, y, rectDim, rectDim);
    }
    else {
	    var newRectDim = rectDim / 2;
	    drawGasket(x, y, newRectDim);
	    drawGasket(x + newRectDim, y, newRectDim);
	    // drawGasket(x, y + newRectDim, newRectDim);
	    drawGasket(x + newRectDim, y + newRectDim, newRectDim);
    }
};
drawGasket(0, 0, rectDim);
</script>