print tree

Author: laileon

src/com/blankj/custom/pretest/PrintTree.java

@@ -0,0 +1,56 @@
+package com.blankj.custom.pretest;
+
+import com.blankj.custom.structure.TreeNode;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class PrintTree {
+    public static void main(String[] args) {
+        TreeNode node0 = new TreeNode(0, null, null);
+        TreeNode node7 = new TreeNode(7, null, null);
+        TreeNode node9 = new TreeNode(9, null, null);
+        TreeNode node1R = new TreeNode(1, null, null);
+        TreeNode node1L = new TreeNode(1, node0, node7);
+        TreeNode node3 = new TreeNode(3, node9, node1R);
+        TreeNode node2 = new TreeNode(2, node1L, node3);
+        printTree(node2);
+    }
+
+    public static void printTree(TreeNode root) {
+        if (root == null)
+            return;
+        Queue<TreeNode> queue = new LinkedList<>();
+
+//        需要额外两个变量。一个变量用来保存当前层 还未打印的结点个数，另一个变量保存下一层待打印的结点个数
+        int current;//当前层 还未打印的结点个数
+        int next;//下一层结点个数
+        StringBuilder nodeVal = new StringBuilder();
+
+        queue.offer(root);
+        current = 1;
+        next = 0;
+        while (!queue.isEmpty()) {
+            TreeNode currentNode = queue.poll();
+            nodeVal.append("(").append(currentNode.val).append(")").append(",");
+            current--;
+
+            if (currentNode.left != null) {
+                //queue加入节点
+                queue.offer(currentNode.left);
+                next++;
+            }
+            if (currentNode.right != null) {
+                //queue加入节点
+                queue.offer(currentNode.right);
+                next++;
+            }
+            if (current == 0) {
+                current = next;
+                next = 0;
+                System.out.println(nodeVal.toString().substring(0, nodeVal.lastIndexOf(",")));
+                nodeVal = new StringBuilder();
+            }
+        }
+    }
+}

src/com/blankj/custom/structure/TreeNode.java

@@ -25,7 +25,7 @@ public class TreeNode {
 
     public TreeNode(int val, TreeNode left, TreeNode right) {
         this.val = val;
-        this.left = null;
-        this.right = null;
+        this.left = left;
+        this.right = right;
     }
 }