701. 二叉搜索树中的插入操作

递归

/**
 * 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) {
        //递归有返回值
        if(root == null ) {
            TreeNode node = new TreeNode(val);
            return node;
        }
        if(root.val > val ) {
            root.left = insertIntoBST(root.left,val);
        }
        if(root.val < val ) {
            root.right = insertIntoBST(root.right,val);
        }
        return root;
    }
}

递归无返回值

/**
 * 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;
    public TreeNode insertIntoBST(TreeNode root, int val) {
        parent = new TreeNode(0);
        if(root == null ) {
            root = new TreeNode(val);
        }
        traversal(root, val );
        return root;
    }
    public void traversal(TreeNode root, int val ) {
        if(root == null ) {
            TreeNode node = new TreeNode(val);
            if(val > parent.val ) parent.right = node;
            else parent.left = node;
            return;
        }
        parent = root;
        if(root.val > val ) traversal(root.left,val);
        if(root.val < val ) traversal(root.right,val);
        return ;
    }
}

迭代

/**
 * 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) {
        //迭代
        if(root == null ) {
            TreeNode node = new TreeNode(val);
            return node;
        }
        TreeNode cur = root;
        TreeNode parent = root;
        while( cur != null ) {
            parent = cur;
            if(cur.val > val) {
                cur = cur.left;
            } else {
                cur = cur.right;
            }
        }
        TreeNode node = new TreeNode(val);
        if(parent.val > val ) {
            parent.left = node;
        } else {
            parent.right = node;
        }
        return root;
    }
}