题解 | #按之字形顺序打印二叉树#

#include <vector>
#include <stack>
/*
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> > res;
        if (!pRoot) {
            return res;
        }
        stack<TreeNode*> m_stack[2];
        int curdigit = 0;//代表奇偶层。0:奇数层 1：偶数层
        int lastdigit = 1;//记录上一次是哪一层
        m_stack[0].push(pRoot);
        while (!m_stack[0].empty() || !m_stack[1].empty()) {
            if (lastdigit == 1) {
                curdigit = 0;
            } else {
                curdigit = 1;
            }
            int row = m_stack[curdigit].size();
            vector<int> m_vec;
            while (row--) {
                TreeNode* node = m_stack[curdigit].top();
                m_stack[curdigit].pop();
                m_vec.push_back(node->val);
                if (curdigit % 2 == 0) {
                    if (node->left) m_stack[1].push(node->left);
                    if (node->right) m_stack[1].push(node->right);
                } else {
                    if (node->right) m_stack[0].push(node->right);
                    if (node->left) m_stack[0].push(node->left);
                }
            }
            lastdigit = curdigit;
            res.push_back(m_vec);
        }
        return res;
    }
};