unique-paths

题目：

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.

程序：

class Solution {public:    int uniquePaths(int m, int n) {        if(m==0&&n==0)            return 0;        if(m==0&&n)            return 1;        if(m&&n==0)            return 1;        vector<vector<int>> dp(m,vector<int>(n,0));        for(int i=0;i<m;i++)            for(int j=0;j<n;j++)                {                    if(i==m-1||j==n-1)                        dp[i][j]=1;                }         for(int i=m-2;i>=0;i--)            for(int j=n-2;j>=0;j--)                {                    dp[i][j]=dp[i+1][j]+dp[i][j+1];                }         return dp[0][0];    }};