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程式語言 - LeetCode - C++ - 103. Binary Tree Zigzag Level Order Traversal

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題目：


解答：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        queue<TreeNode*> st;
        vector<vector<int>> ans;
        int dir = 1;
 
        if (!root) {
            return ans;
        }
 
        st.push(root);
        while (!st.empty()) {
            int size = st.size();
            vector<int> q(size);
 
            for (int i = 0; i < size; ++i) {
                TreeNode *r = st.front();
                st.pop();
 
                if (r->left) {
                    st.push(r->left);
                }
                if (r->right) {
                    st.push(r->right);
                }

                q[dir ? i : size - i - 1] = r->val;
            }
 
            ans.push_back(q);
            dir ^= 1;
        }
 
        return ans;
    }
};