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 > 0:
            top = temp.pop(0)
            newary.append(top.val)
            count -= 1
            if top.left != None:
                temp.append(top.left)
            if top.right != None:
                temp.append(top.right)
        if len(newary) > 0:
            result.append(newary)
        if len(temp) > 0:
            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