94. Binary Tree Inorder Traversal.md

94. Binary Tree Inorder Traversal

Thinking:

• Method:
  • 中序遍历
  • 左 -> 中 -> 右

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        if(root == null) return result;
        inorder(root, result);
        return result;
    }
    private static void inorder(TreeNode n, List<Integer> result){
        if(n == null) return;
        inorder(n.left, result);
        result.add(n.val);
        inorder(n.right, result);
    }
}

Second time

• Method 1: Recursion

   /**
    * Definition for a binary tree node.
    * public class TreeNode {
    *     int val;
    *     TreeNode left;
    *     TreeNode right;
    *     TreeNode(int x) { val = x; }
    * }
    */
   class Solution {
   	private List<Integer> result;
   	public List<Integer> inorderTraversal(TreeNode root) {
   		this.result = new ArrayList<>();
   		dfs(root);
   		return this.result;
   	}
   	private void dfs(TreeNode node){
   		if(node == null) return;
   		dfs(node.left);
   		this.result.add(node.val);
   		dfs(node.right);
   	}
   }