Print a Binary Tree in Vertical Order
http://www.geeksforgeeks.org/print-binary-tree-vertical-order/
1 package algorithms; 2 3 import java.util.ArrayList; 4 import java.util.List; 5 import java.util.Map; 6 import java.util.TreeMap; 7 8 public class PrintVertical { 9 10 private static TreeMap<Integer, List<TreeNode>> hm = new TreeMap<>(); 11 12 public static void main(String[] args) { 13 TreeNode root = new TreeNode(1); 14 TreeNode two = new TreeNode(2); 15 TreeNode three = new TreeNode(3); 16 TreeNode four = new TreeNode(4); 17 TreeNode five = new TreeNode(5); 18 TreeNode six = new TreeNode(6); 19 TreeNode seven = new TreeNode(7); 20 TreeNode eight = new TreeNode(8); 21 TreeNode nine = new TreeNode(9); 22 root.left = two; 23 root.right = three; 24 two.left = four; 25 two.right = five; 26 three.left = six; 27 three.right = seven; 28 six.right = eight; 29 seven.right = nine; 30 printVertical(root); 31 for(Map.Entry<Integer, List<TreeNode>> entry: hm.entrySet()) { 32 System.out.println("key====="+entry.getKey()); 33 List<TreeNode> temp = entry.getValue(); 34 for(TreeNode node: temp){ 35 System.out.println("node val======"+node.val); 36 } 37 } 38 } 39 40 public static void printVertical(TreeNode root) { 41 helper(0, root); 42 } 43 44 public static void helper(int cur, TreeNode root) { 45 if(root == null) 46 return; 47 48 ArrayList<TreeNode> array; 49 if(hm.containsKey(cur)) { 50 array = (ArrayList<TreeNode>) hm.get(cur); 51 } else { 52 array = new ArrayList<TreeNode>(); 53 } 54 array.add(root); 55 hm.put(cur, array); 56 helper(cur - 1, root.left); 57 helper(cur + 1, root.right); 58 } 59 }
<注> 需要注意的是使用TreeMap而不是HashMap来存遍历以后的数据。Better to use TreeMap in this case, as it will store the result in ascending order,
which we are interested in.
