LeetCode 0062 - Unique Paths

Unique Paths

Desicription

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?

fuck!

Above is a 3 x 7 grid. How many possible unique paths are there?

Note: m and n will be at most 100.

Solution

class Solution{
  public:
    int uniquePaths(int m, int n){
        int a = m - 1;
        int b = n + m - 2;
        double res = 1;
        for(int i = 1; i <= a; i++)
            res = res * (b - a + i) / i;
        return res;
    }
};