add print structure in treeNode

Author: zgpeace

code/LeetCode/src/common/TreeNode.java

@@ -1,11 +1,91 @@
 package common;
 
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
 public class TreeNode {
     public int val;
     public TreeNode left;
     public TreeNode right;
-    public TreeNode(int x) {
-        val = x;
+    public TreeNode() { }
+    public TreeNode(int val) {
+        this.val = val;
+    }
+
+    public TreeNode(int val, TreeNode left, TreeNode right) {
+          this.val = val;
+          this.left = left;
+          this.right = right;
     }
 
+    @Override
+    public String toString() {
+        if (this == null) {
+            return "null";
+        }
+
+        String result = "";
+        List<String> row = null;
+        List<List<String>> list = new ArrayList<List<String>>();
+
+        LinkedList<TreeNode> rowNode = new LinkedList<>();
+        rowNode.add(this);
+        while (!rowNode.isEmpty()) {
+            int rowSize = rowNode.size();
+            row = new ArrayList<String>();
+
+            int rowCount = rowSize;
+            int nullCount = 0;
+            while (rowSize > 0) {
+                TreeNode current = rowNode.pop();
+                if (current == null) {
+                    row.add("null");
+                    nullCount++;
+                } else {
+                    row.add(Integer.toString(current.val));
+                }
+
+                if (current == null || current.left == null) {
+                    rowNode.add(null);
+                } else {
+                    rowNode.add(current.left);
+                }
+                if (current == null || current.right == null) {
+                    rowNode.add(null);
+                } else {
+                    rowNode.add(current.right);
+                }
+
+                rowSize--;
+            }
+
+            if (nullCount == rowCount) {
+                break;
+            }
+
+            list.add(row);
+        }
+
+        // print data
+        String blank = "    ";
+        for (int i = 0; i < list.size(); i ++) {
+            for (int j = i; j < list.size(); j++) {
+                // print blank
+                System.out.print(blank);
+            }
+            List<String> rowList = list.get(i);
+            for (int k = 0; k < rowList.size(); k++) {
+                System.out.print(rowList.get(k));
+                System.out.print(blank);
+            }
+
+            System.out.println();
+        }
+
+
+        //return Arrays.toString(list.toArray());
+
+        return super.toString();
+    }
 }