LeetCode - Closest Binary Search Tree Value

ClosestBinarySearchTreeValue.java

// 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.

// use successor and predecessor
public int closestValue(TreeNode root, double target) {
    TreeNode successor = null, predecessor = null;
    
    while(root != null){
        if(root.val > target){
            successor = root;
            root = root.left;
        } else if(root.val < target) {
            predecessor = root;
            root = root.right;
        } else{
            return root.val;
        }
    }
    
    if(successor == null && predecessor == null) return -1;
    if(successor == null) return predecessor.val;
    if(predecessor == null) return successor.val;
    
    if(Math.abs(target - successor.val) < Math.abs(target - predecessor.val)){
        return successor.val;
    } else {
        return predecessor.val;
    }
}

// normal way 
public int closestValue(TreeNode root, double target) {
    if(root == null) return -1;
    int res = root.val;
    while(root != null){
        if(Math.abs(root.val - target) < Math.abs(res - target)){
            res = root.val;
        }
        
        root = root.val > target ? root.left : root.right;
    }
    return res;
}