public static int uniquePaths(int m, int n) {//accepted
        int[][] map = new int[m][n];
        for (int i = 0; i < m; ++i) {
            map[i][0] = 1;
        }
        for (int j = 0; j < n; ++j) {
            map[0][j] = 1;
        }
        for (int i = 1; i < m; ++i) {
            for (int j = 1; j < n; ++j) {
                map[i][j] = map[i-1][j]+map[i][j-1];
            }
        }
        return map[m-1][n-1];
    }