Create 1287-element-appearing-more-than-25-in-sorted-array.js

Author: everthis

1287-element-appearing-more-than-25-in-sorted-array.js

@@ -0,0 +1,50 @@
+/**
+ * @param {number[]} arr
+ * @return {number}
+ */
+const findSpecialInteger = function (arr) {
+  const n = arr.length,
+    { floor } = Math,
+    { getWordIndexRange } = Search()
+  const ticks = [n / 4, n / 2, (n * 3) / 4].map((e) => floor(e))
+  for (const i of ticks) {
+    const [s, e] = getWordIndexRange(arr, arr[i])
+    if (e - s > n / 4) return arr[i]
+  }
+  return 0
+}
+
+function Search() {
+  return { getWordIndexRange }
+
+  /**
+   * Searches for the first true value in the predicate.
+   * Returns hi if not found.
+   * [lo, hi)
+   */
+  function binarySearch(lo, hi, predicate) {
+    while (lo != hi) {
+      let mid = ((lo + hi) / 2) | 0
+      if (predicate(mid)) {
+        hi = mid
+      } else {
+        lo = mid + 1
+      }
+    }
+    return lo
+  }
+
+  function getWordIndexRange(keys, word) {
+    let lo = 0,
+      hi = keys.length
+    function greaterOrEqual(index) {
+      return keys[index] >= word
+    }
+    function less(index) {
+      return keys[index] > word
+    }
+    let lower_bound = binarySearch(0, keys.length, greaterOrEqual)
+    let upper_bound = binarySearch(lower_bound, keys.length, less)
+    return [lower_bound, upper_bound]
+  }
+}