Unique Paths | Problem No. 62 | 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?

Example 1: Input: m = 3, n = 7 Output: 28

Example 2: Input: m = 3, n = 2 Output: 3

Explanation: From the top-left corner, there are a total of 3 ways to reach the bottom-right corner:

1. Right -> Down -> Down
2. Down -> Down -> Right
3. Down -> Right -> Down

Example 3: Input: m = 7, n = 3 Output: 28

Example 4: Input: m = 3, n = 3 Output: 6

Constraints: 1 <= m, n <= 100 It's guaranteed that the answer will be less than or equal to 2 * 109.

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