Java二叉树中LCA问题解决方法两则

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root == null || p == null || q== null){
            return null;
        }
        Stack<TreeNode> stack1 = new Stack<>();
        getPath(root,p,stack1);
        Stack<TreeNode> stack2 = new Stack<>();
        getPath(root,q,stack2);
        int size1 = stack1.size();
        int size2 = stack2.size();
        int size = 0;
        if(size1 > size2){
             size = size1 - size2;
             while(size>0){
                 stack1.pop();
                 size--;
             }
        }
        else{
            size = size2 - size1;
            while(size>0){
                stack2.pop();
                size--;
            }
        }
        //起点已经相同
        while(stack1.peek() != stack2.peek()){
            stack2.pop();
            stack1.pop();
        }
        return stack1.peek();
    }
    public boolean getPath(TreeNode root,TreeNode node,Stack<TreeNode> stack){
        if(root == null || node == null){
            return false;
        }
        stack.push(root);
        if(root == node){
            return true;
        }
        boolean flag1 = getPath(root.left,node,stack);
        if(flag1 == true){
            return true;
        }
        boolean flag2 = getPath(root.right,node,stack);
        if(flag2 == true){
            return true;
        }
        stack.pop();
        return false;
    }
}

class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
       if(root == null ){
           return null;
       }
       if(root == p || root == q){
           return root;
       }
       TreeNode leftT = lowestCommonAncestor(root.left,p,q);
       TreeNode rightT = lowestCommonAncestor(root.right,p,q);
       if(leftT != null && rightT != null){
           return root;
       }
       else if(leftT != null){
           return leftT;
       }
       else if(rightT != null){
           return rightT;
       }
       else{
           return null;
       }
    }
}