题解 | #二叉树的中序遍历#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
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> inorderTraversal(TreeNode* root) {
        vector<int>ret;
        stack<TreeNode *> sta;
        if (!root) {
            return ret;
        }
        TreeNode *head = root;
        while(!sta.empty() || head) {
            // 遍历到最左面
            while (head) {
                sta.push(head);
                head = head->left;
            }
            
            if (!sta.empty()) {
               TreeNode *node = sta.top();
               sta.pop();
               ret.push_back(node->val);
               head = node->right;
            }
        }
        return ret;
        // write code here
    }
};