Add solution #1671

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,463 LeetCode solutions in JavaScript
+# 1,464 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1287,6 +1287,7 @@
 1668|[Maximum Repeating Substring](./solutions/1668-maximum-repeating-substring.js)|Easy|
 1669|[Merge In Between Linked Lists](./solutions/1669-merge-in-between-linked-lists.js)|Medium|
 1670|[Design Front Middle Back Queue](./solutions/1670-design-front-middle-back-queue.js)|Medium|
+1671|[Minimum Number of Removals to Make Mountain Array](./solutions/1671-minimum-number-of-removals-to-make-mountain-array.js)|Hard|
 1672|[Richest Customer Wealth](./solutions/1672-richest-customer-wealth.js)|Easy|
 1679|[Max Number of K-Sum Pairs](./solutions/1679-max-number-of-k-sum-pairs.js)|Medium|
 1716|[Calculate Money in Leetcode Bank](./solutions/1716-calculate-money-in-leetcode-bank.js)|Easy|

solutions/1671-minimum-number-of-removals-to-make-mountain-array.js

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+/**
+ * 1671. Minimum Number of Removals to Make Mountain Array
+ * https://leetcode.com/problems/minimum-number-of-removals-to-make-mountain-array/
+ * Difficulty: Hard
+ *
+ * You may recall that an array arr is a mountain array if and only if:
+ * - arr.length >= 3
+ * - There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that:
+ *   - arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
+ *   - arr[i] > arr[i + 1] > ... > arr[arr.length - 1]
+ *
+ * Given an integer array nums, return the minimum number of elements to remove to make
+ * nums a mountain array.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var minimumMountainRemovals = function(nums) {
+  const length = nums.length;
+  const leftLIS = new Array(length).fill(1);
+  const rightLIS = new Array(length).fill(1);
+
+  for (let i = 1; i < length; i++) {
+    for (let j = 0; j < i; j++) {
+      if (nums[i] > nums[j]) {
+        leftLIS[i] = Math.max(leftLIS[i], leftLIS[j] + 1);
+      }
+    }
+  }
+
+  for (let i = length - 2; i >= 0; i--) {
+    for (let j = length - 1; j > i; j--) {
+      if (nums[i] > nums[j]) {
+        rightLIS[i] = Math.max(rightLIS[i], rightLIS[j] + 1);
+      }
+    }
+  }
+
+  let maxMountainLength = 0;
+  for (let i = 1; i < length - 1; i++) {
+    if (leftLIS[i] > 1 && rightLIS[i] > 1) {
+      maxMountainLength = Math.max(maxMountainLength, leftLIS[i] + rightLIS[i] - 1);
+    }
+  }
+
+  return length - maxMountainLength;
+};