习题练习3: Insert into a Binary Search Tree（二叉搜索树的插入）

题目：Insert into a Binary Search Tree

解法一：递归

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
     
public:
    TreeNode* insertIntoBST(TreeNode* root, int val) {
     
        if(nullptr == root) return new TreeNode(val);
        if(root->val > val){
     
            root->left = insertIntoBST(root->left,val);
        }else{
     
            root->right = insertIntoBST(root->right,val);
        }
        return root;
    }
};

解法二：迭代

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
     
public:
    TreeNode* insertIntoBST(TreeNode* root, int val) {
     
        if(nullptr == root) return new TreeNode(val);
        
        TreeNode* curr = root;
        while(nullptr != curr){
     
            if(curr->val >val){
     
                if(nullptr == curr->left){
     
                    curr->left =  new TreeNode(val);
                    break;
                 }else{
     
                    curr = curr->left;
                }
            }else{
     
                if(nullptr == curr->right){
     
                    curr->right = new TreeNode(val);
                    break;
                }else{
     
                    curr = curr->right;
                }
            }
        }
        return root;
    }
};