Print a Binary Tree Vertical Order (column wise)

最新推荐文章于 2020-09-14 23:05:14 发布

yuanhisn

最新推荐文章于 2020-09-14 23:05:14 发布

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分类专栏： technical interviews BinaryTree

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本文介绍如何使用Java实现一个函数，将给定的二叉树按照列式输出，并且按层次从上到下进行打印。通过使用TreeMap来存储每个列的节点，并递归遍历整棵树，最终输出各列中的所有节点。

This is a Facebook interview question.

We have a binary tree, suppose like this:

8/   \
    610/ \   /  \
  47912/ \
35

We have to print this binary tree in top-down manner - column wise. Note that, 8, 7 & 9 would be considered in same column. So the required output should be:

34658791012

public void traverse(Node root) {
    TreeMap<Integer, List<Integer>> columnMap = new TreeMap<>();

    recurseTraverse(root, columnMap, 0);

    for (Entry<Integer, List<Node<Integer>>> entry: columnMap.entrySet()) {
        System.out.println("Column - " + entry.getKey() + " : " + entry.getValue());
    }
}

private void recurseTraverse(final Node node, final Map<Integer, List<Integer>> columnmap, final int column) {
    if (node == null) {
        return;
    }
    List<Integer> list = columnmap.get(column);
    if (list == null) {
        list = new ArrayList<Integer>();
        columnmap.put(column, list);
    }
    list.add(node.getValue());
    recurse(node.left(), columnmap, column - 1);
    recurse(node.right(), columnmap, column + 1);

}

From:

http://codereview.stackexchange.com/questions/36799/printing-a-binary-tree-top-down-column-wise