Leetcode Binary Tree Level Order Traversal

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]
]

 

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

層次遍歷利用佇列實現即可

vector<vector<int> > levelOrder(TreeNode *root){
    vector<vector<int> > result;
    if(root == NULL) return result;
    queue<TreeNode *> que;
    que.push(root);
    int cnt = 1;
    while(!que.empty()){
        vector<int> row;
        int newCnt = 0;
        while(cnt--){
            TreeNode *node = que.front();que.pop();
            row.push_back(node->val);
            if(node->left) {que.push(node->left); newCnt++;}
            if(node->right) {que.push(node->right); newCnt++;}
        }
        cnt = newCnt;
        result.push_back(row);
    }
    return result;
}