Unique Paths II

Medium

DP · Matrix~20m

00:00

Section 1Understand Problem

Section 01

Understand the problem

Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.

Problem statement

You are given an `m × n` integer array `obstacleGrid`. There is a robot initially located at the top-left corner (`obstacleGrid[0][0]`). The robot tries to move to the bottom-right corner (`obstacleGrid[m-1][n-1]`). The robot can only move either down or right at any point in time. An obstacle and space are marked as `1` or `0` respectively in `obstacleGrid`. A path that the robot takes cannot include any square that is an obstacle. Return the number of possible unique paths that the robot can take to reach the bottom-right corner. The testcases are generated so that the answer will be ≤ 2 · 10⁹.

Example

obstacleGrid = [[0,0,0],[0,1,0],[0,0,0]] → 2

Constraints

m == obstacleGrid.length · n == obstacleGrid[i].length · 1 ≤ m, n ≤ 100 · obstacleGrid[i][j] is 0 or 1

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