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) {
            st.push(root);
        }
        while (!st.empty()) {
                TreeNode* node = st.top();
                vec.push_back(st.top()->val);
                st.pop();
                if (node->right) {
                    st.push(node->right);
                }
                if (node->left) {
                    st.push(node->left);
                }
                
                

        }

        return vec;
    }
};