题解 | #在二叉树中找到两个节点的最近公共祖先#

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @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
        // 定义两个ArrayList 来保存o1,o2的祖先
        ArrayList<Integer> o1Ancetors = new ArrayList<>();
        ArrayList<Integer> o2Ancetors = new ArrayList<>();
        int returnAncetor = -1;
        // 求各自的祖先
        getAncetor(root,o1,o1Ancetors);
        getAncetor(root,o2,o2Ancetors);
        
        for(int i = 0; i< o1Ancetors.size(); i++){
            if(o2Ancetors.contains(o1Ancetors.get(i))){
                    returnAncetor = o1Ancetors.get(i);
                    break;
            }
        }
        return returnAncetor;
        
    }
    
    public boolean getAncetor(TreeNode node,int target,ArrayList<Integer> list){
        if(node == null){
            return false;
        }
        if(node.val == target){
            list.add(node.val);
            return true;
        }
        if(getAncetor(node.left,target,list) || getAncetor(node.right,target,list)){
            list.add(node.val);
            return true;
        }
        return false;
    }
}