Count minimum cost in grid
Last updated: December 12, 2025
Quick Overview
Given a grid of non-negative integers, where each cell represents the cost to enter that cell, write a function to calculate the minimum cost to travel from the top-left corner to the bottom-right corner of the grid. You can only move either down or right at any point in time. The function should return the minimum cost as an integer.
Instacart
December 12, 202522
9
4,397 solved
Given a grid of non-negative integers, where each cell represents the cost to enter that cell, write a function to calculate the minimum cost to travel from the top-left corner to the bottom-right corner of the grid. You can only move either down or right at any point in time. The function should return the minimum cost as an integer.
This coding problem is frequently asked during Onsite at Instacart. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Instacart expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- What is the worst-case input for your solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you optimize the space complexity of your solution?
- How would your solution change if the input was sorted?
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Problem Analysis
This problem can be effectively addressed using Dynamic Programming due to its overlapping subproblems and optimal substructure properties. We want to calculate the minimum cost to reach each cell...
Approach
- Initialize a DP Table: Create a 2D list
dpof the same dimensions as the grid to store the minimum cost to reach each cell. - Base Case: Set
dp[0][0]togrid[0][0]since that is the ...
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