What is Interview Forge?

Interview Forge helps you practice mock interviews, follow study plans, track career goals, review learning analytics, and prepare across 36 pages.

Trapping Rain Water at Microsoft — Interview Guide

How to approach Trapping Rain Water in a Microsoft interview: the optimal approach, what Microsoft interviewers look for, and company-specific tips.

Updated 2026-09HardTwo Pointers / Stack

The problem at Microsoft

Given an array of non-negative heights representing an elevation map, compute how much water can be trapped after raining.

Microsoft uses this problem to assess growth mindset, collaborative, product-minded. Expect Microsoft-specific follow-ups that tie the solution back to production reasoning and the company's engineering bar.

Key concepts

Water above a bar is bounded by the min of the tallest bars to its left and right.
Two pointers exploit that the trapped water at each end depends only on the shorter boundary.
A monotonic decreasing stack also solves it by matching basins.

Approach

def trap(h):
    l, r = 0, len(h) - 1
    left_max = right_max = water = 0
    while l < r:
        if h[l] < h[r]:
            left_max = max(left_max, h[l])
            water += left_max - h[l]
            l += 1
        else:
            right_max = max(right_max, h[r])
            water += right_max - h[r]
            r -= 1
    return water

What Microsoft looks for

Growth mindset — learn from feedback and failure.
Collaboration — how you work across teams.
Customer and product focus — especially for product teams.
Solid CS fundamentals in coding and design.

Unlock the full guide

Premium members get every DSA, system design, company and role interview guide — plus AI practice, mock interviews, and analytics.

Unlock with Premium