D

A

P

```
/*
*
* Unique Paths
*
* There is a robot on an `m x n` grid.
* The robot is initially located at the top-left corner.
* The robot tries to move to the bottom-right corner.
* The robot can only move either down or right at any point in time.
*
* Given the two integers `m` and `n`,
* return the number of possible unique paths that the robot can take to reach the bottom-right corner.
* More info: https://leetcode.com/problems/unique-paths/
*/
/*
* @param {number} m
* @param {number} n
* @return {number}
*/
const uniquePaths = (m, n) => {
// only one way to reach end
if (m === 1 || n === 1) return 1
// build a linear grid of size m
// base case, position 1 has only 1 move
const paths = new Array(m).fill(1)
for (let i = 1; i < n; i++) {
for (let j = 1; j < m; j++) {
// paths[j] in RHS represents the cell value stored above the current cell
// paths[j-1] in RHS represents the cell value stored to the left of the current cell
// paths [j] on the LHS represents the number of distinct pathways to the cell (i,j)
paths[j] = paths[j - 1] + paths[j]
}
}
return paths[m - 1]
}
export { uniquePaths }
```