Monotonic Stack – Next Greater Element (Right)

Problem Statement:

Next Greater Element (to the right): For each element nums[i], find the first element to its right which is strictly greater; if none, return -1.

We use a monotonic decreasing stack of indices: while the current value is greater than the value at the stack top, we can resolve NGE for that top.

Example: nums = [2, 1, 2, 4, 3] → NGE = [4, 2, 4, -1, -1]

Array
NGE
Stack
Stack holds indices of a decreasing sequence by value (top on the right).
Step 0: Initialize empty stack.