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。

/*
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> > ans;
        if (pRoot != NULL) {
        	vector<int> tmp;
            stack<TreeNode*> st;
            stack<TreeNode*> stmp;
            st.push(pRoot);
            TreeNode* cur;
            int tag = 0;
            while (!st.empty()) {
                while (!st.empty()) {
                    cur = st.top();
                    st.pop();
                    tmp.push_back(cur->val);
                    if (tag == 0) {//从右往左 
                        if (cur->left != NULL) {
                            stmp.push(cur->left);
                        }
                        if (cur->right != NULL) {
                            stmp.push(cur->right);
                        }
                    } else {//从左往右
                        if (cur->right != NULL) {
                            stmp.push(cur->right);
                        }
                        if (cur->left != NULL) {
                            stmp.push(cur->left);
                        }
                    }
                }
                tag = 1 - tag;
                ans.push_back(tmp);
                tmp.clear();
                swap(st, stmp);
            }
        }
        return ans;
    }  
    
};