Count of Range Sum problem solved

Author: hasibulislam999

Merge Sort/327_count-of-range-sum.js

@@ -0,0 +1,67 @@
+/**
+ * Title: Count of Range Sum
+ * Description: Given an integer array nums and two integers lower and upper, return the number of range sums that lie in [lower, upper] inclusive. Range sum S(i, j) is defined as the sum of the elements in nums between indices i and j inclusive, where i <= j.
+ * Author: Hasibul Islam
+ * Date: 10/04/2023
+ */
+
+/**
+ * @param {number[]} nums
+ * @param {number} lower
+ * @param {number} upper
+ * @return {number}
+ */
+function SegmentTreeNode(tl, tr) {
+  this.sum = 0;
+  this.left = null;
+  this.right = null;
+  this.tl = tl; // tree left boundary
+  this.tr = tr; // tree right boundary
+}
+
+const build = (a, tl, tr) => {
+  if (tl > tr) return null;
+  let stn = new SegmentTreeNode(a[tl], a[tr]);
+  if (tl == tr) return stn;
+  let mid = (tl + tr) >> 1;
+  stn.left = build(a, tl, mid);
+  stn.right = build(a, mid + 1, tr);
+  return stn;
+};
+
+const update = (stn, newVal) => {
+  if (stn == null) return;
+  if (newVal >= stn.tl && newVal <= stn.tr) {
+    stn.sum++;
+    update(stn.left, newVal);
+    update(stn.right, newVal);
+  }
+};
+
+const sumUtil = (stn, l, r) => {
+  if (stn == null) return 0;
+  if (l <= stn.tl && r >= stn.tr) return stn.sum;
+  if (r < stn.tl || l > stn.tr) return 0;
+  return sumUtil(stn.left, l, r) + sumUtil(stn.right, l, r);
+};
+
+const countRangeSum = (a, lower, upper) => {
+  let an = a.length;
+  let pre = new Set();
+  let sum = 0;
+  for (const e of a) {
+    sum += e;
+    pre.add(sum);
+  }
+  let u = [...pre];
+  let un = u.length;
+  u.sort((x, y) => x - y);
+  let root = build(u, 0, un - 1);
+  let res = 0;
+  for (let i = an - 1; ~i; i--) {
+    update(root, sum);
+    sum -= a[i];
+    res += sumUtil(root, lower + sum, upper + sum);
+  }
+  return res;
+};