235. 二叉搜索树的最近公共祖先

因为是二叉搜索树 所以左边小 右边大
递归

class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
		int pval = p.val;
		int qval = q.val;
		if(root.val>pval&&root.val>qval) return lowestCommonAncestor(root.left, p, q);
    	if(root.val<pval&&root.val<qval) return lowestCommonAncestor(root.right, p, q);
    	return root;
    }
}

递推

class Solution {
  public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
		while(root!=null) {
			int pval = p.val;
			int qval = q.val;
			int rootval = root.val;
			if(rootval > pval&&rootval>qval) {
				root = root.left;
			}
			else if(rootval < pval&&rootval<qval) {
				root = root.right;
			}
			else return root;
		}
    	return null;
    }
}