LeetCode题解之Binary Tree Level Order Traversal II

1、题目描述

2、题目分析

先遍历，再反转。

 

3、代码

vector<vector<int>> levelOrderBottom(TreeNode* root) {
        vector<vector<int>> ans;
        if (root == NULL)
            return ans;
        
        queue<TreeNode*> q;
        q.push(root);
        vector<int> v;
        while (!q.empty()) {
            int size = q.size();
            for (int i = 0; i < size; i++) {
                TreeNode *node = q.front();
                q.pop();
                v.push_back(node->val);
                if (node->left != NULL)
                    q.push(node->left);
                
                if (node->right != NULL)
                    q.push(node->right);
            }
            ans.push_back(v);
            v.clear();
        }
        
        reverse(ans.begin(), ans.end());
        return ans;
    }