把二叉樹列印成多行(六十)

題目描述:

從上到下按層列印二叉樹，同一層結點從左至右輸出。每一層輸出一行。

程式碼(已在牛客上 AC)

思路: BFS

class Solution {
public:
        vector<vector<int> > Print(TreeNode* root) {
            if (!root) return {};
            queue<TreeNode*> q;
            q.push(root);
            vector<vector
 
<int>> res;
            while (!q.empty()) {
                int size = q.size();
                vector<int> cur(size);
                for (int i = 0; i < size; ++i) {
                    auto r = q.front();
                    q.pop();
                    cur[i] = r->val;
                    if
 
 (r->left) q.push(r->left);
                    if (r->right) q.push(r->right);
                }
                res.push_back(cur);
            }
            return res;
        }
};