Compute days until a higher reading
Company: Sonatus
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: hard
Interview Round: Technical Screen
You are given an array `readings[]` representing sensor values over consecutive days (e.g., temperatures).
For each day `i`, compute how many days you must wait until you see a strictly higher reading on a future day `j > i`. If there is no future day with a higher reading, output `0` for that day.
### Input
- An integer array `readings` of length `n`.
### Output
- An integer array `ans` of length `n` where `ans[i]` is the number of days until a higher reading occurs, or `0` if none exists.
### Example
- Input: `readings = [30, 38, 30, 36, 35, 40, 28]`
- Output: `[1, 4, 1, 2, 1, 0, 0]`
### Constraints (typical)
- `1 <= n <= 2e5`
- Readings fit in 32-bit signed integers.
### Notes
- “Higher” means strictly greater (`>`), not greater-or-equal.
Quick Answer: This question evaluates proficiency in array processing and the next-greater-element concept, measuring algorithmic reasoning about sequence traversal, comparisons, and managing time/space trade-offs.
For each index, return how many days until a strictly higher future reading appears. If none appears, return 0 at that index.
Constraints
- Higher means strictly greater
- n can be up to 2e5
Examples
Input: ([30, 38, 30, 36, 35, 40, 28],)
Expected Output: [1, 4, 1, 2, 1, 0, 0]
Input: ([5, 4, 3],)
Expected Output: [0, 0, 0]
Input: ([1, 1, 2],)
Expected Output: [2, 1, 0]
Input: ([],)
Expected Output: []
Hints
- Keep a monotonic decreasing stack of unresolved indices.