java 235.二进制搜索树的最低共同祖先（第1个）.java

Posted 2021-05-08

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

/*
找到的第一个节点，满足（root.val - p.val） * (root.val - q.val) < 0 ，则为LCA
*/
public class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null || p == null || q == null) return null;
        
        //if((root.val >= q.val && root.val <= p.val) || (root.val >= p.val && root.val <= q.val)) {
            //return root;
       
        while((root.val - (long)p.val) * (root.val - (long)q.val) > 0) {// in case of overflow
            root = p.val < root.val ? root.left : root.right;
        }
        return root;
        
    }
}

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