二叉树的层序遍历

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},

    3
   /   9  20
    /     15   7

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

实现代码：

class Solution {
public:
    vector<vector<int> > levelOrder(TreeNode *root) {
        vector<vector<int> > res;
        if(root==NULL) return res;
        queue<TreeNode *> temp;
        temp.push(root);
        while(!temp.empty())
        {
            vector<int> curlevel;
            queue<TreeNode *> nextlevel;
            while(!temp.empty())
            {
                TreeNode* node = temp.front();  
                temp.pop();  
            
                curlevel.push_back(node->val);
                if (node->left != NULL)  nextlevel.push(node->left);
                if (node->right != NULL) nextlevel.push(node->right);
            }
            res.push_back(curlevel);
            temp = nextlevel;
        }
        return res;
    }
};

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,#,#,15,7},

    3
   /   9  20
    /     15   7

return its bottom-up level order traversal as:

[
  [15,7],
  [9,20],
  [3]
]

实现代码：

class Solution {
public:
    vector<vector<int> > levelOrderBottom(TreeNode *root) {
        vector<vector<int> > res;
        if(root==NULL) return res;
        queue<TreeNode *> temp;
        temp.push(root);
        while(!temp.empty())
        {
            vector<int> curlevel;
            queue<TreeNode *> nextlevel;
            while(!temp.empty())
            {
                TreeNode* node = temp.front();  
                temp.pop();  
            
                curlevel.push_back(node->val);
                if (node->left != NULL)  nextlevel.push(node->left);
                if (node->right != NULL) nextlevel.push(node->right);
            }
            res.insert(res.begin(),curlevel);
            temp = nextlevel;
        }
        return res;
    }
};

二叉树的层序遍历

原文：http://blog.csdn.net/wolongdede/article/details/44778341