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Unique Paths

Problem​

There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right at any point in time.

Given the two integers m and n, return the number of possible unique paths that the robot can take to reach the bottom-right corner.

The test cases are generated so that the answer will be less than or equal to 2 * 109.

Solution Approach​

Click - to see solution code
class Solution {
   public:
    int uniquePaths(int m, int n) {
        long long ans = 1;
        if (m > n) swap(m, n);
        for (long long j = m + n - 2; j > n - 1; j--) {
            ans *= j;
            ans /= (m + n - 1 - j);
        }
        return ans;
    }
};