题解 | #把二叉树打印成多行#

/*
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;
            vector<int> ans;
            if(!pRoot)
                return res;
            queue<TreeNode*> q;
            q.push(pRoot);
            ans.push_back(pRoot->val);
            res.push_back(ans); // ans记录下一层的元素
            while(!q.empty()) {
                int n = ans.size();
                ans.clear(); // 将ans中当前层的元素清空
                while(n--) { // 遍历q中当前层的元素
                    auto t = q.front();
                    q.pop();
                    if(t->left) {
                        q.push(t->left);
                        ans.push_back(t->left->val);
                    }
                    if(t->right) {
                        q.push(t->right);
                        ans.push_back(t->right->val);
                    }
                }
                if(ans.size()) // 如果下一层中有元素
                    res.push_back(ans);
            }
            return res;
        }
    
};