剑指Offer打卡day43—— ACWing 88. 树中两个结点的最低公共祖先

Posted 2021-05-25 Johnny*

【题目描述】

ACWing 88. 树中两个结点的最低公共祖先
【思路】

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    /*
    lowestCommonAncestor函数：
    1. 如果p、q都在该子树Tree中则返回该节点
    2. 如果p在该子树中 q不在该子树中，则返回left
    3. 如果q在该子树中 p不在该子树中，则返回right
    */
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        
        
        if( root == null ) return null;
        if( root == p || root == q) return root;
        TreeNode left =  lowestCommonAncestor(root.left, p, q);
        TreeNode right = lowestCommonAncestor(root.right, p, q);
        if(left != null  && right != null)return root;
        if( left != null )  return left;
        return right;
        
    }
}