题解 | 二叉树的中序遍历|迭代法

/**
 * 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> inorderTraversal(TreeNode* root) {
        // write code here
        stack<TreeNode*> st;
        vector<int> res;
        TreeNode* curr = root;
        while (curr || !st.empty()) {
            while (curr) {
                st.push(curr);
                curr = curr->left;
            }
            curr = st.top();
            st.pop();
            res.push_back(curr->val);
            curr = curr->right;
        }
        return res;
    }
};