sorting

Author: sohail0992

searchAlgrothems/quickSort/index.js

@@ -0,0 +1,51 @@
+// O (n 2) worst case
+
+function swap(a ,b) {
+    const temp = a;
+    a = b;
+    b = temp;
+}
+
+function partition(arr, first, last) {
+    const pivot = first;
+    let lowerIndex = first + 1;
+    let upperIndex = last;
+     // call first element as pivot
+    // loop till the higher and lower indices cross each other
+    while (upperIndex >= lowerIndex) {
+        if (arr[pivot] > arr[lowerIndex]) {
+            lowerIndex++;
+        } else if (arr[upperIndex] > arr[pivot]) {
+            upperIndex--;
+        } else if (arr[pivot] > arr[upperIndex] && arr[lowerIndex] > arr[upperIndex]) {
+            // now lower index value is greater than pivot so we stop incrementing the lowerindex
+            // we will decrement the upperIndex until we find a value that is less than pivot and lowerindex value we will switch array indices positions
+            const temp = arr[upperIndex];
+            arr[upperIndex] = arr[lowerIndex];
+            arr[lowerIndex] = temp;
+            upperIndex--;
+            lowerIndex++;
+        }
+    }
+    // swap pivot with uper
+    const temp = arr[upperIndex];
+    arr[upperIndex] = arr[pivot];
+    arr[pivot] = temp;
+    return upperIndex;
+}
+
+function quickSort(arr, first, last) {
+    if (first < last) {
+        const pivot = partition(arr, first, last);
+        quickSort(arr, first, pivot - 1);
+        quickSort(arr, pivot + 1, last);
+    }
+}
+
+
+const arr = [20, 6, 8, 53, 23, 87, 42, 19];
+console.log(arr, 'orignal');
+quickSort(arr, 0, (arr.length - 1));
+console.log(arr, 'sorted');
+
+module.exports = quickSort;