85. Insert Node in a Binary Search Tree【easy】

Given a binary search tree and a new tree node, insert the node into the tree. You should keep the tree still be a valid binary search tree.

Notice

You can assume there is no duplicate values in this tree + node.

 

Example

Given binary search tree as follow, after Insert node 6, the tree should be:

  2             2
 /            / 
1   4   -->   1   4
   /             /  
  3             3   6

Challenge

Can you do it without recursion?

解法一：

public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    public TreeNode insertNode(TreeNode root, TreeNode node) {
        if (root == null) {
            return node;
        }
        if (root.val > node.val) {
            root.left = insertNode(root.left, node);
        } else {
            root.right = insertNode(root.right, node);
        }
        return root;
    }
}

解法二：

public class Solution {
    /**
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    public TreeNode insertNode(TreeNode root, TreeNode node) {
        if (root == null) {
            root = node;
            return root;
        }
        TreeNode tmp = root;
        TreeNode last = null;
        while (tmp != null) {
            last = tmp;
            if (tmp.val > node.val) {
                tmp = tmp.left;
            } else {
                tmp = tmp.right;
            }
        }
        if (last != null) {
            if (last.val > node.val) {
                last.left = node;
            } else {
                last.right = node;
            }
        }
        return root;
    }
}

解法三：

class Solution {
public:
    /*
     * @param root: The root of the binary search tree.
     * @param node: insert this node into the binary search tree
     * @return: The root of the new binary search tree.
     */
    TreeNode * insertNode(TreeNode * root, TreeNode * node) {
        stack<TreeNode * > sta;
        sta.push(root);
        TreeNode * last = NULL;
        while (sta.size() != 0) {
            TreeNode * now = sta.top();
            sta.pop();
            if (now == NULL) {
                if (last == NULL) {
                    root = node;
                } else if (last->val <= node->val) {
                    last -> right = node;
                } else {
                    last -> left = node;
                }
                break;
            } else if (now->val <= node->val) {
                sta.push(now->right);
            } else {
                sta.push(now->left);
            }
            last = now;
        }
        return root;
    }
};

参考@DLNU-linglian 的代码