JAVA 二叉树遍历，

JAVA 二叉树遍历，

二叉树的定义如下：

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

递归的版本很简单，下面仅列出非递归的版本。

//先序遍历
public void searchPreOrder(TreeNode root) {
        Stack<TreeNode> s = new Stack<TreeNode>();
        if (root == null) {
            return;
        }
        while (root != null) {
            System.out.println(root.val);
            if (root.right != null) {
                s.push(root.right);
            }
            if (root.left != null) {
                root = root.left;
            } else {
                if (s.isEmpty()) {
                    break;
                }
                root = s.pop();
            }
        }

    }

//中序遍历
    public void searchMidOrder(TreeNode root) {
        Stack<TreeNode> s = new Stack<TreeNode>();
        while (root != null || (!s.isEmpty())) {
            while (root != null) {
                s.push(root);
                root = root.left;
            }
            if (!s.isEmpty()) {
                root = s.pop();
                System.out.print(root.val + " ");
                root = root.right;
            }
        }
    }

//后序遍历
    public void searchPostOrder(TreeNode root) {
        Stack<TreeNode> s = new Stack<TreeNode>();
        TreeNode t = null;
        int flag = 1;
        if (root == null) {
            return;
        }
        do {
            while (root != null) {
                s.push(root);
                root = root.left;
            }
            t = null;
            flag = 1;
            while ((!s.isEmpty()) && (flag == 1)) {
                root = s.peek();
                if (root.right == t) {
                    System.out.println(root.val);
                    t = root;
                    s.pop();
                } else {
                    root = root.right;
                    flag = 0;
                }
            }
        } while (!s.isEmpty());
    }

//层次遍历
public void levelSearch(TreeNode root) {
        Queue<TreeNode> s = new LinkedList<TreeNode>();
        if (root == null) {
            return;
        }
        s.add(root);
        while (!s.isEmpty()) {
            TreeNode t = s.poll();
            System.out.println(t.val);
            if (t.left != null) {
                s.add(t.left);
            }
            if (t.right != null) {
                s.add(t.right);
            }
        }
    }

在这做个记录，方便以后查阅。