[刷题]Binary Tree Inorder Traversal

最新推荐文章于 2022-03-31 17:31:26 发布

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本文详细介绍了二叉树中序遍历的两种方法：递归和分治。通过实例演示了如何使用这两种方法实现中序遍历，并解释了每种方法的原理和优缺点。

[LintCode]Binary Tree Inorder Traversal

VERSION I Divide & Conquer

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Inorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
        // 2015-3-22 DFS
        ArrayList<Integer> rst = new ArrayList<>();
        if (root == null) {
            return rst;
        }
        
        // divide
        ArrayList<Integer> left = inorderTraversal(root.left);
        ArrayList<Integer> right = inorderTraversal(root.right);
        
        // conquer
        rst.addAll(left);
        rst.add(root.val);
        rst.addAll(right);
        
        return rst;
    }
}

VERSION II Recursion

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Inorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
        // 2015-4-1 recursion
        ArrayList<Integer> rst = new ArrayList<>();
        if (root == null) {
            return rst;
        }
        
        rst.addAll(inorderTraversal(root.left));
        rst.add(root.val);
        rst.addAll(inorderTraversal(root.right));
        
        return rst;
    }
}