이진 트리, Binary Tree inorder Traversal

Problems

• 94. Binary Tree Inorder Traversal

Given the root of a binary tree, return the inorder traversal of its nodes’ values. Constraints:

• The number of nodes in the tree is in the range [0, 100].
• -100 <= Node.val <= 100

  문제 해석

Inorder 순회를 하면서 각 노드의 값을 출력하라

문제 접근

• inorder traversal : LEFT SELF RIGHT
• Recursion

/**
 * 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<Integer> inorderTraversal(TreeNode root) {
       List<Integer> ret = new ArrayList<>();
       traverse(root, ret);
       return ret;
    }

    public static void traverse(TreeNode root, List<Integer> ret){
	    if(root == null) return;
	    traverse(root.left);
	    //self
	    ret.add(root.val);
	    traverse(root.right);
    }
}