diff --git a/2001-2100/2058. Find the Minimum and Maximum Number of Nodes Between Critical Points.md b/2001-2100/2058. Find the Minimum and Maximum Number of Nodes Between Critical Points.md new file mode 100644 index 0000000..1694447 --- /dev/null +++ b/2001-2100/2058. Find the Minimum and Maximum Number of Nodes Between Critical Points.md @@ -0,0 +1,116 @@ +# 2058. Find the Minimum and Maximum Number of Nodes Between Critical Points + +- Difficulty: Medium. +- Related Topics: Linked List. +- Similar Questions: . + +## Problem + +A **critical point** in a linked list is defined as **either** a **local maxima** or a **local minima**. + +A node is a **local maxima** if the current node has a value **strictly greater** than the previous node and the next node. + +A node is a **local minima** if the current node has a value **strictly smaller** than the previous node and the next node. + +Note that a node can only be a local maxima/minima if there exists **both** a previous node and a next node. + +Given a linked list `head`, return **an array of length 2 containing **`[minDistance, maxDistance]`** where **`minDistance`** is the **minimum distance** between **any two distinct** critical points and **`maxDistance`** is the **maximum distance** between **any two distinct** critical points. If there are **fewer** than two critical points, return **`[-1, -1]`. + +  +Example 1: + +![](https://assets.leetcode.com/uploads/2021/10/13/a1.png) + +``` +Input: head = [3,1] +Output: [-1,-1] +Explanation: There are no critical points in [3,1]. +``` + +Example 2: + +![](https://assets.leetcode.com/uploads/2021/10/13/a2.png) + +``` +Input: head = [5,3,1,2,5,1,2] +Output: [1,3] +Explanation: There are three critical points: +- [5,3,1,2,5,1,2]: The third node is a local minima because 1 is less than 3 and 2. +- [5,3,1,2,5,1,2]: The fifth node is a local maxima because 5 is greater than 2 and 1. +- [5,3,1,2,5,1,2]: The sixth node is a local minima because 1 is less than 5 and 2. +The minimum distance is between the fifth and the sixth node. minDistance = 6 - 5 = 1. +The maximum distance is between the third and the sixth node. maxDistance = 6 - 3 = 3. +``` + +Example 3: + +![](https://assets.leetcode.com/uploads/2021/10/14/a5.png) + +``` +Input: head = [1,3,2,2,3,2,2,2,7] +Output: [3,3] +Explanation: There are two critical points: +- [1,3,2,2,3,2,2,2,7]: The second node is a local maxima because 3 is greater than 1 and 2. +- [1,3,2,2,3,2,2,2,7]: The fifth node is a local maxima because 3 is greater than 2 and 2. +Both the minimum and maximum distances are between the second and the fifth node. +Thus, minDistance and maxDistance is 5 - 2 = 3. +Note that the last node is not considered a local maxima because it does not have a next node. +``` + +  +**Constraints:** + + + +- The number of nodes in the list is in the range `[2, 105]`. + +- `1 <= Node.val <= 105` + + + +## Solution + +```javascript +/** + * Definition for singly-linked list. + * function ListNode(val, next) { + * this.val = (val===undefined ? 0 : val) + * this.next = (next===undefined ? null : next) + * } + */ +/** + * @param {ListNode} head + * @return {number[]} + */ +var nodesBetweenCriticalPoints = function(head) { + var firstPoint = -1; + var lastPoint = -1; + var last = null; + var now = head; + var i = 0; + var minDistance = Number.MAX_SAFE_INTEGER; + while (now) { + if (last && now.next && ((now.val > last.val && now.val > now.next.val) || (now.val < last.val && now.val < now.next.val))) { + if (firstPoint === -1) firstPoint = i; + if (lastPoint !== -1) minDistance = Math.min(minDistance, i - lastPoint); + lastPoint = i; + } + last = now; + now = now.next; + i += 1; + } + if (firstPoint !== -1 && lastPoint !== -1 && lastPoint !== firstPoint) { + return [minDistance, lastPoint - firstPoint]; + } + return [-1, -1]; +}; +``` + +**Explain:** + +nope. + +**Complexity:** + +* Time complexity : O(n). +* Space complexity : O(n).