Create 1157-online-majority-element-in-subarray.js

Author: everthis

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

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+/**
+ * @param {number[]} arr
+ */
+const MajorityChecker = function(arr) {
+  const map = new Map()
+  for (let i = 0; i < arr.length; i++) {
+    if (!map.has(arr[i])) map.set(arr[i], [i])
+    else map.get(arr[i]).push(i)
+  }
+  this.pos = map
+  this.arr = arr
+}
+
+function lbs(arr, val) {
+  let lo = 0
+  let hi = arr.length - 1
+  if (arr[0] >= val) return 0
+  else if (arr[hi] < val) return Infinity
+  let mid
+  while (hi - lo > 1) {
+    mid = (hi + lo) >> 1
+    if (arr[mid] === val) return mid
+    else if (arr[mid] < val) lo = mid
+    else if (arr[mid] > val) hi = mid
+  }
+  return hi
+}
+
+function rbs(arr, val) {
+  let lo = 0
+  let hi = arr.length - 1
+  if (arr[hi] <= val) return hi
+  else if (arr[lo] > val) return -Infinity
+  let mid
+  while (hi - lo > 1) {
+    mid = (hi + lo) >> 1
+    if (arr[mid] === val) return mid
+    else if (arr[mid] < val) lo = mid
+    else if (arr[mid] > val) hi = mid
+  }
+  return lo
+}
+
+/**
+ * @param {number} left
+ * @param {number} right
+ * @param {number} threshold
+ * @return {number}
+ */
+MajorityChecker.prototype.query = function(left, right, threshold) {
+  const { arr, pos } = this
+  let c = 20
+  while (c--) {
+    const idx = left + Math.floor(Math.random() * (right - left + 1))
+    const sort = pos.get(arr[idx])
+    const lidx = lbs(sort, left)
+    const ridx = rbs(sort, right)
+    if (ridx - lidx + 1 >= threshold) return arr[idx]
+  }
+  return -1
+}
+
+/**
+ * Your MajorityChecker object will be instantiated and called as such:
+ * var obj = new MajorityChecker(arr)
+ * var param_1 = obj.query(left,right,threshold)
+ */