CloestBinarySearchTreeValue.java

private double curMinDelta = Double.MAX_VALUE;
    private int smallestValue = 0;

    public int closestValue(TreeNode root, double target) {
        this.searchMin(root, target);
        return this.smallestValue;
    }

    private void searchMin(TreeNode root, double target) {
        if (root == null) {
            return;
        }

        if (target == root.val) {
            this.smallestValue = root.val;
            return;
        }

        double delta = Math.abs(target - root.val);
        if (delta < this.curMinDelta) {
            smallestValue = root.val;
            this.curMinDelta = delta;
        }

        if (target < root.val) {
            this.searchMin(root.left, target);
        } else {
            this.searchMin(root.right, target);
        }
    }