不同的路径

class Solution {
public:
    /**
     * @param n, m: positive integer (1 <= n ,m <= 100)
     * @return an integer
     */
    int uniquePaths(int m, int n) {
        // wirte your code here
        int a[m][n];
        for(int i = 0; i < m; ++i)
            a[i][0] = 1;
        for(int j = 0; j < n; ++j)
            a[0][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];
    }
};

ps：a[i][j]=a[i-1][j]+a[i][j-1]