leetcode62 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.

class Solution {
public:
    int uniquePaths(int m, int n) {
/*      if(n==1)
            return 1;
        int ans=0;
        vector<int> jlist(n-1,1);
        for(int i=1;i<m;i++)
        {
            for(int j=0;j<n-1;j++)
            {
                if(j==0)
                    jlist[j]++;
                else
                    jlist[j]+=jlist[j-1];
            }
        }
        return jlist[n-2];*/
        int ans=0;
        vector<int> jlist(n,1);
        for(int i=1;i<m;i++)
        {
            for(int j=1;j<n;j++)
                jlist[j]+=jlist[j-1];
        }
        return jlist[n-1];
    }
};