public static int findMaximum(int[][] mat)
{
    if(mat.length==0 || mat[0][0]==-1){ return -1; }
    return findMaximum(mat,0,0);
}

public static int findMaximum(int[][] mat, int i ,int j)
{
    if( i>=mat.length || j>=mat[0].length  || j<0 || i<0 || mat[i][j]==-1) { return 0;}

    int temp = mat[i][j];
    mat[i][j] = -1;

    int down = 0;int left = 0; int right = 0;
    if( i%2==0)
    {
        right = temp + findMaximum(mat, i, j+1);
        down = temp + findMaximum(mat, i + 1, j);
    }

    else
    {
        left = temp + findMaximum(mat, i , j-1);
        down = temp + findMaximum(mat, i + 1, j);
    }

    mat[i][j] = temp;

    return Math.max(down, Math.max(left, right));

}