Kth Largest Element in Array

Author: charlesbuczel

0215_kthLargetElementInArray.js

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+/**
+ * @param {number[]} nums Unsorted array of numbers.
+ * @param {number} k Kth largets element in array to return.
+ * @return {number} Value of kth largest element in array.
+ * @summary Kth Largest Element in an Array {@link https://leetcode.com/problems/kth-largest-element-in-an-array/}
+ * @description Given unsorted array of numbers, return its kth largest element.
+ * Space O(1) - Not creating any new arrays.
+ * Time O(n) - in worst case N^2.
+ */
+const findKthLargest = (nums, k) => {
+  const size = nums.length;
+
+  const generateRandom = upTo => Math.floor(Math.random() * upTo);
+
+  const partition = (left, right, pivot) => {
+    let pivotValue = nums[pivot];
+
+    [nums[pivot], nums[right]] = [nums[right], nums[pivot]];
+
+    let index = left;
+
+    for (let i = left; i <= right; i++) {
+      if (nums[i] < pivotValue) {
+        [nums[index], nums[i]] = [nums[i], nums[index]];
+        index++;
+      }
+    }
+
+    [nums[index], nums[right]] = [nums[right], nums[index]];
+
+    return index;
+  };
+
+  const quickselect = (left, right, target) => {
+    if (left === right) nums[left];
+
+    let pivot = left + generateRandom(right - left + 1);
+
+    pivot = partition(left, right, pivot);
+
+    if (target === pivot) return nums[target];
+    else if (target < pivot) return quickselect(left, pivot - 1, target);
+    return quickselect(pivot + 1, right, target);
+  };
+
+  return quickselect(0, size - 1, size - k);
+};