leetcode102

本题是广度优先遍历（BFS）实现树的层次遍历，使用队列实现。

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> res;
        queue<TreeNode*>q;
        if (root != NULL)
        {
            q.push(root);
            while (!q.empty())
            {
                vector<int> tmp;
                vector<TreeNode*> T;
                while (!q.empty())
                {
                    TreeNode* t = q.front();
                    q.pop();
                    tmp.push_back(t->val);
                    if (t->left != NULL)
                    {
                        T.push_back(t->left);
                    }
                    if (t->right != NULL)
                    {
                        T.push_back(t->right);
                    }
                }
                res.push_back(tmp);
                for (auto x : T)
                {
                    q.push(x);
                }
            }
        }
        return res;
    }
};

补充一个python的实现：

 class Solution:
     def lOrder(self,temp,result):
         count = len(temp)
         newary = []
         while count > :
             top = temp.pop()
             newary.append(top.val)
             count -=
             if top.left != None:
                 temp.append(top.left)
             if top.right != None:
                 temp.append(top.right)
         if len(newary) > :
             result.append(newary)
         if len(temp) > :
             self.lOrder(temp,result)

     def levelOrder(self, root: TreeNode) -> List[List[int]]:
         result = []
         temp = []
         if root != None:
             temp.append(root)
             self.lOrder(temp,result)
         return result