[LeetCode Medium] BST - Insert into a Binary Search Tree

 

/**
 * 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 {
    
    TreeNode parent = null;
    int flag = -1;
    
    public TreeNode insertIntoBST(TreeNode root, int val) {
        TreeNode result = insert(root, val);	        
		return result;
    }
	
	private TreeNode insert(TreeNode root, int val) {        
        
		if(root == null) {	// 최초에 빈 BST or 리프블록까지 온 경우
			root = new TreeNode(val);  // 신규 Node
            		if(flag == 0) parent.right = root;	// 오른쪽에 insert
            		if(flag == 1) parent.left = root;	// 왼쪽에 insert
            		return root;
		}
		if(root.val < val) {	// 오른쪽
            		flag = 0;
            		parent = root;
			insert(root.right, val);
        }
		else if (root.val > val) {	// 왼쪽
            		flag = 1;
            		parent = root;
			insert(root.left, val);
        }
		
		return root;
	}
}

 

다시 푼거

/**
 * 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 TreeNode insertIntoBST(TreeNode root, int val) {
        if(root == null) {  // 빈 트리면 루트 노트로 삽입
            return new TreeNode(val);            
        }               
        
        if(root.val < val) {
            root.right = insertIntoBST(root.right, val);
        }
        
        if(root.val > val) {
            root.left = insertIntoBST(root.left, val);
        }
        
        return root; 
    }
}

 

BST 삽입/삭제 참고 => https://youtu.be/xxADG17SveY