Java-为什么我的递归Draw树方法无法正确输出

Question

I implemented a heap using an array and i'm trying to draw a tree out of the elements in the array. Here is my method.

public void DrawTree(Job[] a,int index,int pre_space){
    for (int i=0;i<pre_space;i++)
           System.out.print(" ");

System.out.print(a[index].getName()+":"+index );

if (2*index<=element_count&&2*index+1<=element_count){ //if it has both children
        System.out.println();

    for (int i=0;i<pre_space;i++)
            System.out.print(" ");

    System.out.print("/");
    System.out.println("\\");

        DrawTree(a,2*index,pre_space-8);
    DrawTree(a,2*index+1,3);

    }

else if (2*index<=element_count){ //if it only has a left child

System.out.println();

for (int i=0;i<pre_space;i++)
            System.out.print(" ");

    System.out.println("/");
        DrawTree(a,2*index,pre_space-3);

     }


    }

I am outputting the index as well for understandability. Here is the output I got:

          whateve:1
          /\
  Robin:2
  /
Roudy:4   Romy:3

Romy should be on the same line as Robin, and from what I understand, when I call the DrawTree method for the right child(Romy) it will backtrack to the appropriate line.

Answer 1

As stated in the comment, the scheme you are using is a pre-order traversal, so for example if we have a tree :

              1
             / \
            2   3
           / \
          4   5

When you traverse to node 2, you output some additional lines before you can go to node 3.

The order is 1 -> output some line ->2 -> output some lines -> 4 -> 5 ->3, so at node 3, we now has at least 2 lines between node 1 and 3.

So what you should do is using an ArrayList<ArrayList<String>> lines , with each element ArrayList<String> in lines represent one line.

Note : this problem is far complicated than your current implementation as between each level of the tree, we need to give enough space to display all of its successors. So you need to pre-calculate the necessary space (depending on the size of the sub-tree at each node) before print them out.