sum between k1th and k2th smallest elements

Author: manju07

Data-Structure/Heap/sumBetweenK1nK2.js

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+'use strict';
+function minHeapify(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;
+        minHeapify(arr, smallestIndex, n);
+    }
+}
+
+function findSumBetweenK1nK2(arr, k1, k2) {
+    // construct min heap
+    for (let index = (arr.length / 2) - 1; index >= 0; index--)
+        minHeapify(arr, index, arr.length)
+
+    for (let index = 0; index < k1; index++) {
+        minHeapify(arr, 0, arr.length - index);
+        let temp = arr[0];
+        arr[0] = arr[arr.length - 1 - index];
+        arr[arr.length - 1 - index] = temp;
+    }
+    let sum = 0;
+    for (let index = k1; index < (k2 - 1); index++) {
+        minHeapify(arr, 0, arr.length - index);
+        sum = sum + arr[0];
+        let temp = arr[0];
+        arr[0] = arr[arr.length - 1 - index];
+        arr[arr.length - 1 - index] = temp;
+    }
+    return sum;
+}
+//  Sum of elements between k1th and k2th smallest elements
+let array = [20, 8, 22, 4, 12, 10, 14];
+let k1 = 3, k2 = 6;
+// k1th smallest element is 10, k2th smallest element is 20
+// and sum between these two elements are [12, 14] = 26
+console.log('sum between ' + k1 + ' and ' + k2 + ' smallest elements is = ' + findSumBetweenK1nK2(array, k1, k2))