Unique Paths [LeetCode]

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.

Solution: Pretty easy, use dynamic programming, from bottom line to top line, caculate every the path num of every cell.

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