Add solution #1157

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,157 LeetCode solutions in JavaScript
+# 1,158 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -905,6 +905,7 @@
 1154|[Day of the Year](./solutions/1154-day-of-the-year.js)|Easy|
 1155|[Number of Dice Rolls With Target Sum](./solutions/1155-number-of-dice-rolls-with-target-sum.js)|Medium|
 1156|[Swap For Longest Repeated Character Substring](./solutions/1156-swap-for-longest-repeated-character-substring.js)|Medium|
+1157|[Online Majority Element In Subarray](./solutions/1157-online-majority-element-in-subarray.js)|Hard|
 1161|[Maximum Level Sum of a Binary Tree](./solutions/1161-maximum-level-sum-of-a-binary-tree.js)|Medium|
 1189|[Maximum Number of Balloons](./solutions/1189-maximum-number-of-balloons.js)|Easy|
 1200|[Minimum Absolute Difference](./solutions/1200-minimum-absolute-difference.js)|Easy|

solutions/1157-online-majority-element-in-subarray.js

@@ -0,0 +1,77 @@
+/**
+ * 1157. Online Majority Element In Subarray
+ * https://leetcode.com/problems/online-majority-element-in-subarray/
+ * Difficulty: Hard
+ *
+ * Design a data structure that efficiently finds the majority element of a given subarray.
+ *
+ * The majority element of a subarray is an element that occurs threshold times or more in
+ * the subarray.
+ *
+ * Implementing the MajorityChecker class:
+ * - MajorityChecker(int[] arr) Initializes the instance of the class with the given array arr.
+ * - int query(int left, int right, int threshold) returns the element in the subarray
+ *   arr[left...right] that occurs at least threshold times, or -1 if no such element exists.
+ */
+
+/**
+ * @param {number[]} arr
+ */
+var MajorityChecker = function(arr) {
+  this.positionMap = new Map();
+  this.array = arr;
+  for (let i = 0; i < arr.length; i++) {
+    const positions = this.positionMap.get(arr[i]) || [];
+    positions.push(i);
+    this.positionMap.set(arr[i], positions);
+  }
+};
+
+/**
+ * @param {number} left
+ * @param {number} right
+ * @param {number} threshold
+ * @return {number}
+ */
+MajorityChecker.prototype.query = function(left, right, threshold) {
+  const maxAttempts = 20;
+  const rangeLength = right - left + 1;
+
+  for (let attempt = 0; attempt < maxAttempts; attempt++) {
+    const candidate = this.array[left + Math.floor(Math.random() * rangeLength)];
+    const positions = this.positionMap.get(candidate);
+    const count = countInRange(positions, left, right);
+
+    if (count >= threshold) return candidate;
+    if (count + rangeLength - count < threshold) return -1;
+  }
+  return -1;
+};
+
+function countInRange(positions, left, right) {
+  const leftIndex = lowerBound(positions, left);
+  const rightIndex = upperBound(positions, right);
+  return rightIndex - leftIndex;
+}
+
+function lowerBound(arr, target) {
+  let start = 0;
+  let end = arr.length;
+  while (start < end) {
+    const mid = Math.floor((start + end) / 2);
+    if (arr[mid] < target) start = mid + 1;
+    else end = mid;
+  }
+  return start;
+}
+
+function upperBound(arr, target) {
+  let start = 0;
+  let end = arr.length;
+  while (start < end) {
+    const mid = Math.floor((start + end) / 2);
+    if (arr[mid] <= target) start = mid + 1;
+    else end = mid;
+  }
+  return start;
+}