leetcode-----107. 二叉树的层次遍历 II

• 链接：https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/

代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        vector<vector<int>> ans;
        queue<TreeNode*> q;
        if (root) q.push(root);
        while (q.size()) {
            vector<int> level;
            int len = q.size();
            while (len--) {
                auto t = q.front();
                q.pop();
                level.push_back(t->val);
                if (t->left) q.push(t->left);
                if (t->right) q.push(t->right);
            }
            ans.push_back(level);
        }
        reverse(ans.begin(), ans.end());
        return ans;
    }
};