find k largest elements and kth largest element

Author: manju07

Data-Structure/Tree/Heap/kLargestElements.js

@@ -0,0 +1,40 @@
+'use strict';
+function heapify(arr, rootIndex, n) {
+    let smallestIndex = rootIndex;
+    let leftIndex = (rootIndex * 2) + 1;
+    let rightIndex = (rootIndex * 2) + 2;
+    if (leftIndex < n && arr[smallestIndex] > arr[leftIndex]) smallestIndex = leftIndex;
+    if (rightIndex < n && arr[smallestIndex] > arr[rightIndex]) smallestIndex = rightIndex;
+    if (smallestIndex != rootIndex) {
+        let temp = arr[rootIndex];
+        arr[rootIndex] = arr[smallestIndex];
+        arr[smallestIndex] = temp;
+        heapify(arr, smallestIndex, n);
+    }
+}
+
+function kLargestElements(array, k) {
+    // Build Min Heap of size K
+    for (let index = parseInt(k / 2) - 1; index >= 0; index--)
+        heapify(array, index, k);
+
+    for (let index = k; index < array.length; index++) {
+        if (array[0] < array[index]) {
+            array[0] = array[index];
+            heapify(array, 0, k);
+        }
+    }
+}
+
+let array = [3, 5, 1, 8, 2, 4, 10, 12, 0, 7, 13, 16];
+let k = 3;
+kLargestElements(array, k);
+let kLargestElemetsStr = '';
+for (let index = 0; index < k; index++) {
+    if (index == (k - 1))
+        kLargestElemetsStr = kLargestElemetsStr + array[index];
+    else
+        kLargestElemetsStr = kLargestElemetsStr + array[index] + ', ';
+}
+console.log(k, ' largest elements are - ', kLargestElemetsStr);
+console.log(k + 'th largest element is - ', array[0]);