1 int uniquePaths(int m, int n) { 2         vector<int> sum(n, 0); 3          4         sum[n - 1] = 1; 5         for (int i = m - 1; i >= 0; i--) 6             for (int j = n - 2; j >= 0; j--) 7                 sum[j] += sum[j + 1]; 8                  9         return sum[0];10 }