LeetCode. 二叉树的最近公共祖先（树遍历+用栈存两条路径+寻找路径中的节点）

给定一个二叉树, 找到该树中两个指定节点的最近公共祖先。

struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};
#include 
using namespace std;
class Solution {
public:
	TreeNode * lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
		TreeNode * result = nullptr;
		//p_result和q_result为搜索到的路径
		vector<TreeNode*> path, p_result, q_result;
		int finish_test = 0;//记录是否找到节点
		preorder(root, p, path, p_result, finish_test);
		path.clear();
		finish_test = 0;
		preorder(root, q, path, q_result, finish_test);
        
        //找出短路径的长度
		unsigned path_len;
		if(p_result.size() < q_result.size())
			path_len = p_result.size();
		else
			path_len = q_result.size();
        
        //遍历路径，一步步找到最邻近的公共祖先
		for (unsigned i = 0; i < path_len; i++)
			if (p_result.at(i) == q_result.at(i))
				result = p_result.at(i);
		return result;
	}
private:
    //线序遍历查找路径
	static void preorder(           //树中查询节点
		TreeNode* node,
		TreeNode* search,
		vector<TreeNode*> &path,    //遍历时节点路径栈
		vector<TreeNode*> &result,  //最终搜索到节点search的路径结果
		int& finish                 //是否找到节点search的变量，未找到时是0，找到是1
	)
	{ 
		if(!node || finish) {       //node为空||已找到search变量
			return;
		}
		path.push_back(node);
		if (node == search){
			finish = 1;
			result = path;
		}
		preorder(node->left, search, path, result, finish);
		preorder(node->right, search, path, result, finish);
		path.pop_back();
	}
};