Closest Binary Search Tree Value

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

Note:

• Given target value is a floating point.
• You are guaranteed to have only one unique value in the BST that is closest to the target.

10/17/2015 Update Iteration version

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int closestValue(TreeNode* root, double target) {
        int ans = root->val;
        while(root != nullptr){
            ans = fabs(target - ans) < fabs(target - root->val)? ans: root->val;
            if(target > root->val){
                root = root->right;
            }
            else{
                root = root->left;
            }
        }
        return ans;
    }
};

Recursive version

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int closestValue(TreeNode* root, double target) {
        int tmp;
        if(target > root->val && root->right){
            tmp = closestValue(root->right, target);
        }
        else if(target < root->val && root->left){
            tmp = closestValue(root->left, target);
        }
        else{
            return root->val;
        }
        
        return abs(tmp - target) < abs(root->val - target)? tmp: root->val;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int closestValue(TreeNode* root, double target) {
        int ans = root->val;
        BST(root, ans, target);
        return ans;
    }
    void BST(TreeNode * root, int & ans, double target){
        if(root == NULL) return ;
        if(abs(root->val - target) < abs(ans - target)){
            ans = root->val;
        }
        if(root->val < target){//BUG HERE , root->val not ans
            BST(root->right, ans, target);
        }
        else if (root->val > target){
            BST(root->left, ans, target);
        }
        else{
            return ;
        }
    }
};