【剑指offer】面试题32（1）：从上往下不分行打印二叉树

完整代码地址

题目

思路

代码

public class _32_01_PrintTreeFromTopToBottom {

public static class TreeNode {
public int val = 0;
public TreeNode left = null;
public TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}

public static ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
if(root == null)
return new ArrayList<>();

ArrayList<Integer> list = new ArrayList<>();
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);

while(!queue.isEmpty()) {
TreeNode node = queue.poll();
list.add(node.val);
if(node.left != null)
queue.add(node.left);
if(node.right != null)
queue.add(node.right);
}
return list;
}
}

测试

public class _32_01_Test {

public static void main(String[] args) {
test1();
test2();
test3();
}

/**
* 功能测试
*     1
*    / \
*   2   3
*  / \   \
* 4   5   6
*/
private static void test1() {
TreeNode root = new TreeNode(1);
TreeNode node2 = new TreeNode(2);
TreeNode node3 = new TreeNode(3);
TreeNode node4 = new TreeNode(4);
TreeNode node5 = new TreeNode(5);
TreeNode node6 = new TreeNode(6);
root.left = node2;
root.right = node3;
node2.left = node4;
node2.right = node5;
node3.right = node6;
System.out.println(_32_01_PrintTreeFromTopToBottom.PrintFromTopToBottom(root));
}

/**
* 边界测试
* 1.只有一个节点
* 2.每个节点都只有左子节点
* 3.每个节点都只有右子节点
*/
private static void test2() {
TreeNode root = new TreeNode(1);

System.out.println(_32_01_PrintTreeFromTopToBottom.PrintFromTopToBottom(root));

TreeNode node2 = new TreeNode(2);
TreeNode node3 = new TreeNode(3);
root.left = node2;
node2.left = node3;

System.out.println(_32_01_PrintTreeFromTopToBottom.PrintFromTopToBottom(root));

root.left = null;
node2.left = null;
root.right = node2;
node2.right = node3;
System.out.println(_32_01_PrintTreeFromTopToBottom.PrintFromTopToBottom(root));
}

/**
* 极端测试
* null
*/
private static void test3() {
System.out.println(_32_01_PrintTreeFromTopToBottom.PrintFromTopToBottom(null));
}

}