代码随想录算法训练营第十四天|二叉树part01| 递归遍历

144.二叉树的前序遍历 Binary Tree Preorder Traversal - LeetCode

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List preorderTraversal(TreeNode root) {
        List list = new ArrayList<>();
        preorderTraversal(root, list);
        return list;
    }

    private void preorderTraversal(TreeNode root, List list) {
        if (root == null) return;
        list.add(root.val);
        preorderTraversal(root.left, list);
        preorderTraversal(root.right, list);
    }
}

145.二叉树的后序遍历 Binary Tree Postorder Traversal - LeetCode

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List postorderTraversal(TreeNode root) {
        List list = new ArrayList<>();
        postorderTraversal(root, list);
        return list;
    }

    private void postorderTraversal(TreeNode root, List list) {
        if (root == null) return;
        postorderTraversal(root.left, list);
        postorderTraversal(root.right, list);
        list.add(root.val);
    }
} 

 94.二叉树的中序遍历Binary Tree Inorder Traversal - LeetCode

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List inorderTraversal(TreeNode root) {
        List list = new ArrayList<>();
        inorderTraversal(root, list);
        return list;
    }

    private void inorderTraversal(TreeNode root, List list) {
        if (root == null) return;
        inorderTraversal(root.left, list);
        list.add(root.val);
        inorderTraversal(root.right, list);
    }
}