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.

测试时间2ms算法

class Solution {public:    int tab[101][101];        int C(int m,int n){        if(m==0 || m==n) return 1;        if(tab[m][n]) return tab[m][n];        int res = C(m-1,n-1) + C(m,n-1);        tab[m][n] = res;        return res;    }        int uniquePaths(int m, int n) {        return C(m-1,n+m-2);    }};