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🔥Trapping Rain Water: Monotonic Elevation TrapHard
SUPER HARD PROBLEM OF THE DAY+150 XP • FAANG OA TIER
High-difficulty challenge matching authentic Google, Amazon & Uber L5 online assessment conditions.
HardTwo Pointers•Acceptance: 61.2%
Trapping Rain Water: Monotonic Elevation Trap
Targeted in FAANG & Tech OA:GoogleAmazonMicrosoft
Real-World Engineering Context
Applied in GIS topographical hydrology modelling and reservoir watershed simulations at Google Maps and Earth Engine to calculate surface water runoff retention.
Given `n` non-negative integers representing an elevation map where the width of each bar is `1`, compute how much water it can trap after raining.
Water can only be trapped between two higher boundaries. The trapped water at any index is `min(maxLeft, maxRight) - height[i]`.
Sample Test Cases
Input: [[0,1,0,2,1,0,1,3,2,1,2,1]]
Expected: 6
Input: [[4,2,0,3,2,5]]
Expected: 9
Input: [[3,3,3,3]]
Expected: 0
Constraints
- n == height.length
- 1 <= n <= 2 * 10^4
- 0 <= height[i] <= 10^5
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