day21

1、235. 二叉搜索树的最近公共祖先

class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root.val > p.val && root.val > q.val){
            return lowestCommonAncestor(root.left, p, q);
        } else if (root.val < p.val && root.val < q.val) {
            return lowestCommonAncestor(root.right, p, q);
        } else {
            return root;
        }
    }
}

2、701.二叉搜索树中的插入操作

class Solution {
    public TreeNode insertIntoBST(TreeNode root, int val) {
        TreeNode addNode = new TreeNode(val);

        if(root == null){
            root = addNode;
        }

        if(root.val > val){
            root.left = insertIntoBST(root.left, val);
        }
        if(root.val < val){
            root.right = insertIntoBST(root.right, val);
        }
        return root;
    }   
}

3、450.删除二叉搜索树中的节点

class Solution {
    public TreeNode deleteNode(TreeNode root, int key) {
        if(root == null ) {
            return root;
        }

        if(root.val == key) {
            if(root.left == null){
                return root.right;
            } else if(root.right == null){
                return root.left;
            }else {
                TreeNode cur = root.right;
                while(cur.left != null){
                    cur = cur.left;
                } 
                cur.left = root.left;
                root = root.right;
                return root;
            }
        }

        if(root.val > key ) {
            root.left = deleteNode(root.left, key);
        }
        if(root.val < key) {
            root.right = deleteNode(root.right, key);
        }

        return root;
    }
}