Write a function that given a BST, it will return the distance (number of edges) between 2 nodes.

For example, given this tree

         5
        / \
       3   6
      / \   \
     2   4   7
    /         \
   1           8

The distance between1and4is 3:[1 -> 2 -> 3 -> 4]

The distance between1

public int bstDistance(TreeNode root, int node1, int node2) {
    if (root == null) return -1;
    TreeNode lca = lca(root, node1, node2);
    return getDistance(lca, node1) + getDistance(lca, node2);
}

private int getDistance(TreeNode src, int
 
 dest) {
    if (src.val == dest) return 0;
    TreeNode node = src.left;
    if (src.val < dest) {
        node = src.right;
    }
    return 1 + getDistance(node, dest);
}

private TreeNode lca(TreeNode root, int node1, int node2) {
    while (true) {
        if (root.val > node1 && root.val > node2) {
            root 
 
= root.left;
        } else if (root.val < node1 && root.val < node2) {
            root = root.right;
        } else {
            return root;
        }
    }
}

Javasolution:
Time complexity:O(h), wherehis the height of the tree.
Space complexity:O(h).

找到LCA---計算LCA到兩個node的距離並相加