[数据结构与算法]力扣算法学习day16-3

力扣算法学习day16-3

235-二叉搜索树的最近公共祖先

题目

代码实现

/**
 * 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(p.val < root.val && q.val < root.val){
            return lowestCommonAncestor(root.left,p,q);
        } else if(p.val > root.val && q.val > root.val){
            return lowestCommonAncestor(root.right,p,q);
        } else{
            return root;
        }

    }
}

701-二叉搜索树中的插入操作

题目

代码实现

/**
 * 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){
    //         TreeNode temp = new TreeNode(val);
    //         root = temp;
    //     } else{
    //         insertNode(root,val);
    //     }

    //     return root;
    // }
    // public void insertNode(TreeNode node,int val){

    //     if(val < node.val){ 
    //         if(node.left == null){
    //             TreeNode temp = new TreeNode(val);
    //             node.left = temp;
    //             return;
    //         }
    //         insertNode(node.left,val);
    //     }

    //     if(val > node.val){
    //         if(node.right == null){
    //             TreeNode temp = new TreeNode(val);
    //             node.right = temp;
    //             return;
    //         }
    //         insertNode(node.right,val);
    //     }
    // }

    // 迭代法：
    public TreeNode insertIntoBST(TreeNode root, int val) {
        if (root == null) return new TreeNode(val);
        TreeNode head = root;
        TreeNode pre = root;
        while (root != null) {
            pre = root;
            if (root.val > val) {
                root = root.left;
            } else if (root.val < val) {
                root = root.right;
            } 
        }
        if (pre.val > val) {
            pre.left = new TreeNode(val);
        } else {
            pre.right = new TreeNode(val);
        }

        return head;
    }
}

450-做了大半，错误，明日修改。