以下是使用递归和非递归方式实现二叉树先序遍历的代码示例：
使用递归实现先序遍历：
class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int val) {
this.val = val;
}
}
public class BinaryTreeTraversalExample {
public static void preOrderTraversal(TreeNode root) {
if (root == null) {
return;
}
System.out.print(root.val + " ");
preOrderTraversal(root.left);
preOrderTraversal(root.right);
}
public static void main(String[] args) {
// 构建二叉树
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.left = new TreeNode(4);
root.left.right = new TreeNode(5);
// 执行先序遍历
preOrderTraversal(root);
}
}
使用非递归实现先序遍历（使用栈）：
class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int val) {
this.val = val;
}
}
public class BinaryTreeTraversalExample {
public static void preOrderTraversalNonRecursive(TreeNode root) {
if (root == null) {
return;
}
Stack<TreeNode> stack = new Stack<>();
stack.push(root);
while (!stack.isEmpty()) {
TreeNode node = stack.pop();
System.out.print(node.val + " ");
if (node.right!= null) {
stack.push(node.right);
}
if (node.left!= null) {
stack.push(node.left);
}
}
}
public static void main(String[] args) {
// 构建二叉树
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.left = new TreeNode(4);
root.left.right = new TreeNode(5);
// 执行先序遍历
preOrderTraversalNonRecursive(root);
}
}
这只是简单的示例代码，实际应用中可能还需要根据具体需求进行更多的优化和处理。你可以根据自己的需求对代码进行修改和扩展。
