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).
这道题就是动态规划，每做一步算出有多少种，代码如下：

class Solution {
public:
    int uniquePaths(int m, int n) {
        int a[m][n];
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                a[i][j]=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];
    }
};