Next Greater Node In Linked List
<p>You are given the <code>head</code> of a linked list with <code>n</code> nodes.</p>

<p>For each node in the list, find the value of the <strong>next greater node</strong>. That is, for each node, find the value of the first node that is next to it and has a <strong>strictly larger</strong> value than it.</p>

<p>Return an integer array <code>answer</code> where <code>answer[i]</code> is the value of the next greater node of the <code>i<sup>th</sup></code> node (<strong>1-indexed</strong>). If the <code>i<sup>th</sup></code> node does not have a next greater node, set <code>answer[i] = 0</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1000-1099/1019.Next%20Greater%20Node%20In%20Linked%20List/images/linkedlistnext1.jpg" style="width: 304px; height: 133px;" />
<pre>
<strong>Input:</strong> head = [2,1,5]
<strong>Output:</strong> [5,5,0]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1000-1099/1019.Next%20Greater%20Node%20In%20Linked%20List/images/linkedlistnext2.jpg" style="width: 500px; height: 113px;" />
<pre>
<strong>Input:</strong> head = [2,7,4,3,5]
<strong>Output:</strong> [7,0,5,5,0]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the list is <code>n</code>.</li>
	<li><code>1 &lt;= n &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= Node.val &lt;= 10<sup>9</sup></code></li>
</ul>
Stack; Array; Linked List; Monotonic Stack
// Definition for singly-linked list.
// #[derive(PartialEq, Eq, Clone, Debug)]
// pub struct ListNode {
//   pub val: i32,
//   pub next: Option<Box<ListNode>>
// }
//
// impl ListNode {
//   #[inline]
//   fn new(val: i32) -> Self {
//     ListNode {
//       next: None,
//       val
//     }
//   }
// }
use std::collections::VecDeque;
impl Solution {
    pub fn next_larger_nodes(head: Option<Box<ListNode>>) -> Vec<i32> {
        let mut nums = Vec::new();
        let mut current = &head;
        while let Some(node) = current {
            nums.push(node.val);
            current = &node.next;
        }

        let mut stk = VecDeque::new();
        let n = nums.len();
        let mut ans = vec![0; n];
        for i in (0..n).rev() {
            while !stk.is_empty() && stk.back().copied().unwrap() <= nums[i] {
                stk.pop_back();
            }
            if let Some(&top) = stk.back() {
                ans[i] = top;
            }
            stk.push_back(nums[i]);
        }
        ans
    }
}
