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235. 二叉搜索树的最近公共祖先

题目链接: 二叉搜索树的最近公共祖先

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

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

701.二叉搜索树中的插入操作

题目链接: 二叉搜索树中的插入操作

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/**
 * 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) {
            return new TreeNode(val);
        }

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

        return root;
    }
}

450.删除二叉搜索树中的节点

题目链接: 删除二叉搜索树中的节点

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/**
 * 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 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;
    }
}