题解 | #二叉树的前序遍历#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
#include <stack>
#include <vector>
class Solution {
public:
    /**
     * 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 
     * @return int整型vector
     */
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        vector<int> vec;
        stack<TreeNode*> st;
        if (root == nullptr) {
            return vec;
        }
        st.push(root);
        while (!st.empty()) {
            TreeNode* node = st.top();
            st.pop();
            vec.push_back(node->val);
            if (node->right) {
                st.push(node->right);
            }
            if (node->left) {
                st.push(node->left);
            }
 
        }

        return vec;;
    }
};