#62 - Unique Paths

Medium • View on LeetCode • View on GitHub

Problem Description

There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). 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.

Solution

/**
 * @param {number} m
 * @param {number} n
 * @return {number}
 */
var uniquePaths = function(m, n) {
  const row = new Array(n);

  for (let i = 0; i < n; i++) {
    row[i] = 1;
  }

  for (let i = 1; i < m; i++) {
    for (let j = 1; j < n; j++) {
      row[j] += row[j - 1];
    }
  }

  return row[n - 1];
};