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(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
    vector<vector<int> > Print(TreeNode* pRoot) {
        stack<TreeNode*> s1; // 奇数层节点
        stack<TreeNode*> s2; // 偶数层节点
        vector<vector<int> > res;
        if(pRoot)
            s1.push(pRoot);
        while(s1.size() || s2.size()) {
            vector<int> ans; // 每一层的节点的值
            while(s1.size()) {
                auto t = s1.top();
                s1.pop();
                ans.push_back(t->val); // 将节点值压入ans中
                if(t->left)
                    s2.push(t->left);
                if(t->right)
                    s2.push(t->right);
            }
            if(ans.size())
                res.push_back(ans); // 将奇数层数据压入res
            ans.clear(); // 清空ans中的数据
            while(s2.size()) {
                auto t = s2.top();
                s2.pop();
                ans.push_back(t->val);
                if(t->right)
                    s1.push(t->right);
                if(t->left)
                    s1.push(t->left);
            }
            if(ans.size())
                res.push_back(ans); // 将偶数层节点的值压入res;
        }
        return res;
    }
};