LeetCode - Binary Tree Inorder Traversal [Java]

• 문제 링크 : Binary Tree Inorder Traversal

Binary Tree Inorder Traversal - LeetCode

 

정답(Solution)

 

Stack 풀이

/**
 * 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;
 *     }
 * }
 */
import java.util.*;
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> answer = new ArrayList<>();
        Stack<TreeNode> stack = new Stack();
        while(root != null || !stack.isEmpty()){
            while(root != null){
                stack.push(root);
                root = root.left;
            }
            root = stack.pop();
            answer.add(root.val);
            root = root.right;
        }
        return answer;
    }
}

 

재귀 풀이

import java.util.*;

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> iList = new ArrayList<>();

        dfs(root, iList);

        return iList;
    }

    private void dfs(TreeNode root, List<Integer> iList){
        if(root == null){
            return;
        }
        dfs(root.left, iList);
        iList.add(root.val);
        dfs(root.right, iList);
    }
}

 

분석

• DFS
• 가장 기본적인 개념의 풀이