Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
For example:Given binary tree [3,9,20,null,null,15,7],
3 / \ 9 20 / \ 15 7
return its bottom-up level order traversal as:
[ [15,7], [9,20], [3] ]--------------------------------------------------------------------------------
这个就是二叉树的层序遍历，和leetcode102. Binary Tree Level Order Traversal类似，只是要把最后得到的二维数组逆转一下就成。
C++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) { if(!root) return {}; queue<TreeNode*> q; q.push(root); vector<vector<int> > vec; while(!q.empty()){ vector<int> v;; for(int i = q.size(); i > 0; i--){ auto t = q.front(); q.pop(); v.push_back(t->val); if(t->left) q.push(t->left); if(t->right) q.push(t->right); } vec.push_back(v); } reverse(vec.begin(),vec.end()); return vec; } };
转载于:https://www.cnblogs.com/Weixu-Liu/p/10786286.html
