按之字形顺序打印二叉树

题目描述

请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。

AC代码

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
    vector<vector<int> > Print(TreeNode* pRoot) {
        vector<vector<int> > vec;
        if (pRoot == NULL) {
            return vec;
        }
        stack<TreeNode*> s1, s2;
        s1.push(pRoot);
        while (!s1.empty() || !s2.empty()) {
            vector<int> vec1;
            TreeNode *cur;
            while (!s1.empty()) {
                cur = s1.top();
                vec1.push_back(cur->val);
                if (cur->left) {
                    s2.push(cur->left);
                }
                if (cur->right) {
                    s2.push(cur->right);
                }
                s1.pop();
            }
            if (!vec1.empty()) {
                vec.push_back(vec1);
            }
            vector<int> vec2;
            while (!s2.empty()) {
                cur = s2.top();
                vec2.push_back(cur->val);
                if (cur->right) {
                    s1.push(cur->right);
                }
                if (cur->left) {
                    s1.push(cur->left);
                }
                s2.pop();
            }
            if (!vec2.empty()) {
                vec.push_back(vec2);
            }
        }
        return vec;
    } 
};

思路

使用双栈的结构.左右横跳(先进后出)符合之字形,使用两个栈解决存放问题.

或者一个队列,设一个奇偶flag,一下子是按left right进子节点,一下子按right left进子节点并记录size 然后每行pop就行(感觉有点麻烦)