BST_solution_iterative.java

        public int closestValue(TreeNode root, double target) {
            long minVal = Long.MAX_VALUE;
            while(root != null){
                if(Math.abs(root.val - target) < Math.abs(minVal - target)){
                    minVal = root.val;
                }
                if(target < root.val) root = root.left;
                else root = root.right;
            }
            return minVal == Long.MAX_VALUE ? 0 : (int) minVal;
        }