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?

Above is a 3 x 7 grid. How many possible unique paths are there?

Note: m and n will be at most 100.

public class Solution {    public int uniquePaths(int m, int n) {        if(n==0||m==0)return 0;        int [][] a = new int[m][n];        for(int i =0;i<n;i++){            a[0][i]=1;        }        for(int i =0;i<m;i++){            a[i][0]=1;        }        for(int i=1;i<m;i++){            for(int j =1;j<n;j++){                a[i][j]=a[i-1][j]+a[i][j-1];            }        }        return a[m-1][n-1];    }}