题解 | #在二叉树中找到两个节点的最近公共祖先#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    
    int LCA = -1;
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param o1 int整型 
     * @param o2 int整型 
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int o1, int o2) {
        // write code here
        findLCA(root,o1,o2);
        return LCA;
    }

    private int findLCA(TreeNode root, int o1, int o2) {
        // TODO
        if(root==null){
            return 0;
        }
        int res = 0;
        if(root.val == o1){
            res+=1;
        }
        if(root.val == o2){
            res+=2;
        }
        int res1 = findLCA(root.left,o1,o2);
        int res2 = findLCA(root.right,o1,o2);
        if(res1==3||res2==3){
            return 3;
        }else{
            res = res + res1 + res2;
            if(res == 3 && LCA==-1){
                LCA = root.val;
            }
            return res;
        }
    }
}