Binary Tree Level Order Traversal

问题描述

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).

For example:

Given binary tree {3,9,20,#,#,15,7},



return its level order traversal as:

代码

struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

vector<vector<int>> levelOrder(TreeNode* root) {
deque<TreeNode*>a;
deque<TreeNode*>b;
if (root)
a.push_back(root);

TreeNode*p = NULL;
vector<vector<int>> result;

while (!a.empty())
{
vector<int>temp;
if (!a.empty() )
{
while (!a.empty() )
{
p = a.front();
a.pop_front();
temp.push_back(p->val);
if (p->left)
b.push_back(p->left);
if (p->right)
b.push_back(p->right);
}
result.push_back(temp);
}

while (!b.empty())
{
a.push_back(b.front());
b.pop_front();
}
}
return result;
}