What is the time and space complexity of Next Greater Element I?

Time complexity: O(n + m). Space complexity: O(n).

Next Greater Element I

Easy

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Solution Guide: Next Greater Element I

Approach

Process nums2 with a monotonic decreasing stack. When current value is greater than stack top, it becomes the next greater element for popped values. Store this in a map, then answer nums1 queries from the map.

Complexity Analysis

Time: O(n + m)
Space: O(n)

Pattern

Monotonic Stack + Hash Map

Why It Works

The stack keeps values waiting for a larger element. The first value that pops them is their nearest greater element to the right.

Updated Feb 2026