题解 | #按之字形顺序打印二叉树#

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
#include <algorithm>
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 pRoot TreeNode类
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > Print(TreeNode* pRoot) {
        // write code here
        vector<vector<int>> w;
        if (pRoot == nullptr) return w;
        queue<TreeNode*> tree;
        stack<TreeNode*>st;
        int flag = 0;
        tree.push(pRoot);
        while (!tree.empty()) {
            vector<int> v;
            int size = tree.size();
            while (size--) {
                pRoot = tree.front();
                tree.pop();
                v.push_back(pRoot->val);
                if (pRoot->left) tree.push(pRoot->left);
                if (pRoot->right) tree.push(pRoot->right);
            }
            if (flag % 2 == 1) {
                reverse(v.begin(), v.end());
            }
            flag++;
            w.push_back(v);

        }
        return w;
    }
};

层次遍历的基础上对奇数层，反转。