题解 | #二叉搜索树的最近公共祖先#

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 {
    /**
     * 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 p int整型
     * @param q int整型
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int p, int q) {
        // write code here
        Map<Integer, Integer> map = new HashMap<>();
        TreeNode first = root, second = root;
        while (first.val != p) {
            map.put(first.val, 0);
            if (first.val < p) {
                first = first.right;
            } else {
                first = first.left;
            }
        }
        map.put(p, 0);
        int ans = root.val;
        while (second.val != q) {
            if (map.containsKey(second.val)) {
                ans = second.val;
            }
            if (second.val < q) {
                second = second.right;
            } else {
                second = second.left;
            }
        }
        if (map.containsKey(q)) {
            ans = q;
        }
        return ans;
    }
}