思路:和之前的由上向下的层次遍历一样,只需要改变一下输出的顺序即可。
class Solution {
public:
vector<vector<int>> levelOrderBottom(TreeNode* root) {
if(!root) return {};
vector<vector<int> > ans;
queue<TreeNode*> q;
q.push(root);
while(!q.empty())
{
vector<int> tmp;
int size=q.size();
for(int i=0;i<size;++i)
{
TreeNode* t=q.front();q.pop();
tmp.push_back(t->val);
if(t->left) q.push(t->left);
if(t->right) q.push(t->right);
}
ans.insert(ans.begin(),tmp);
}
return ans;
}
};