62. Unique Paths

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).

How many possible unique paths are there?

Example:

Input: m=3, n=2
Output: 3

Input: m=7, n=3
Output: 28

Follow up: 63. Unique Paths II

/**
 * @param {number} m
 * @param {number} n
 * @return {number}
 */
var uniquePaths = function(m, n) {
  if(m===1||n===1) return 1
  var dp=[]
  for(var i=0;i<m;i++) {
    dp[i]=[]
    for(var j=0;j<n;j++) {
      M[i][j] = (M[i-1][j]||1) + (M[i][j-1]||1)
    }
  }
  return M[m-1][n-1]
}