二叉树遍历

最新推荐文章于 2024-10-21 08:57:50 发布

gzvincentlee

最新推荐文章于 2024-10-21 08:57:50 发布

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分类专栏：剑指offer

本文链接：https://blog.youkuaiyun.com/gzvincentlee/article/details/48935515

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本文介绍了二叉树的三种遍历方法：前序、中序和后序遍历，并提供了具体的非递归及递归实现代码。前序遍历采用栈结构实现，中序遍历同样使用栈来辅助完成，而后序遍历则直接通过递归方式实现。

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前序遍历：非递归解法

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Preorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> preorderTraversal(TreeNode root) {
        // write your code here
        ArrayList<Integer> result = new ArrayList<Integer>();
        Stack<TreeNode> stack = new Stack<TreeNode>();
        if(root == null){
            return result;
        }
        stack.push(root);
        while(!stack.empty()){
            TreeNode temp = stack.pop();
            result.add(temp.val);
            if(temp.right!=null){
                stack.push(temp.right);
            }
            if(temp.left!=null){
                stack.push(temp.left);
            }
        }
        return result;
    }
}

中序遍历：非递归解法

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Inorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
        // write your code here
        ArrayList<Integer> result = new ArrayList<Integer>();
        Stack<TreeNode> stack = new Stack<TreeNode>();
        TreeNode cur = root;
        while(cur != null || !stack.empty()){
            while(cur != null){
                stack.push(cur);
                cur = cur.left;
            }
            cur = stack.peek();
            result.add(cur.val);
            stack.pop();
            cur = cur.right;
        }
        return result;
    }
}

后续遍历：递归解法

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Postorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> postorderTraversal(TreeNode root) {
        // write your code here
        ArrayList<Integer> result = new ArrayList<Integer>();
        if(root == null){
            return result;
        }
        result.addAll(postorderTraversal(root.left));
        result.addAll(postorderTraversal(root.right));
        result.add(root.val);
        return result;
    }
}