Give a binary tree, elegantly print it so that no two tree nodes share the same column. Requirement: left child should appear on the left column of root, and right child should appear on the right of root.Example:     a   b   c d   e   fz g   h i j

这道题若能发现inorder traversal each node的顺序其实就是column number递增的顺序，那么就成功了一大半

维护一个global variable，colNum, 做inorder traversal

然后level order 一层一层打印出来

1 package uberOnsite; 2  3 import java.util.*; 4  5 public class PrintTree { 6     public static class TreeNode { 7         char val; 8         int col; 9         TreeNode left;10         TreeNode right;11         public TreeNode(char value) {12             this.val = value;13         }14     }15     16     static int colNum = 0;17     18     public static List
     
       print(TreeNode root) {19         List
      
        res = new ArrayList
       
        ();20         if (root == null) return res;21         inorder(root);22         levelOrder(root, res);23         return res;24     }25     26     public static void inorder(TreeNode node) {27         if (node == null) return;28         inorder(node.left);29         node.col = colNum;30         colNum++;31         inorder(node.right);32         33     }34     35     public static void levelOrder(TreeNode node, List
        
          res) {36         Queue
         
           queue = new LinkedList
          
           ();37 queue.offer(node);38 while (!queue.isEmpty()) {39 StringBuilder line = new StringBuilder();40 HashMap
           
             lineMap = new HashMap
            
             ();41 int maxCol = Integer.MIN_VALUE;42 int size = queue.size();43 for (int i=0; i
             
               res = print(A);90 for (String each : res) {91 System.out.println(each);92 }93 }94 95 }