leetcode-master/problems/0589.N叉树的前序遍历.md

题目地址

https://leetcode-cn.com/problems/n-ary-tree-preorder-traversal/

思路

递归C++代码

class Solution {
private:
    vector<int> result;
    void traversal (Node* root) {
        if (root == NULL) return;
        result.push_back(root->val);
        for (int i = 0; i < root->children.size(); i++) {
            traversal(root->children[i]);
        }
    }

public:
    vector<int> preorder(Node* root) {
        result.clear();
        traversal(root);
        return result;
    }
};

迭代法C++代码

class Solution {

public:
    vector<int> preorder(Node* root) {
        vector<int> result;
        if (root == NULL) return result;
        stack<Node*> st;
        st.push(root);
        while (!st.empty()) {
            Node* node = st.top();
            st.pop();
            result.push_back(node->val);
            // 注意要倒叙，这样才能达到前序（中左右）的效果
            for (int i = node->children.size() - 1; i >= 0; i--) {
                if (node->children[i] != NULL) {
                    st.push(node->children[i]);
                }
            }
        }
        return result;
    }
};