题解 | #按之字形顺序打印二叉树#

BFS 广度优先遍历

/*
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>> r;
        if (pRoot == nullptr) return r;
        queue<TreeNode*> q;
        q.push(pRoot);
        int level = 0;
        while (!q.empty()){
            int sz = q.size();
            vector<int> ans;
            while(sz--){
                TreeNode* node = q.front();
                q.pop();
                ans.push_back(node->val);
                if(node->left) q.push(node->left);
                if(node->right) q.push(node->right);
            }
            ++level;
            if((level & 1) == 0){
                reverse(ans.begin(), ans.end());
            }
            r.push_back(ans);
        }
        return r;
    }
    
};