题解 | #按之字形顺序打印二叉树#C++版

C++版，两个栈解决方案

/*
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 == nullptr) return res;
        vector<int> lvec;
        stack<TreeNode*> stk[2];
        stk[0].push(pRoot);
        TreeNode* p = nullptr;
        for(int i = 0; !stk[i].empty(); i = (i+1) % 2) {
            lvec.clear();
            while (!stk[i].empty()) {
                p = stk[i].top();
                stk[i].pop();
                lvec.push_back(p->val);
                if(i == 0){
                    if(p->left) stk[1].push(p->left);
                    if(p->right) stk[1].push(p->right);
                }else{
                    if(p->right) stk[0].push(p->right);
                    if(p->left) stk[0].push(p->left);
                }
            }
            res.push_back(lvec);
        }
        return res;
    }
    
};