給出一棵二叉樹，返回其節(jié)點值的層次遍歷（逐層從左往右訪問）
樣例
給一棵二叉樹 {3,9,20,#,#,15,7} ：
3
/
9 20
/
15 7
返回他的分層遍歷結(jié)果：
[
[3],
[9,20],
[15,7]
]
分析：
廣度優(yōu)先遍歷沦偎，隊列
/**
* Definition of TreeNode:
* class TreeNode {
* public:
* int val;
* TreeNode *left, *right;
* TreeNode(int val) {
* this->val = val;
* this->left = this->right = NULL;
* }
* }
*/
class Solution {
/**
* @param root: The root of binary tree.
* @return: Level order a list of lists of integer
*/
public:
vector<vector<int>> levelOrder(TreeNode *root) {
vector<vector<int>>result;
if (root == NULL) {
return result;
}
// write your code here
deque<TreeNode *>oneQueue;
TreeNode *head = root;
oneQueue.push_back(head);
int currentLevel = 0;
int currentLevelInternalCount = 1;
int nextLevelInternalCount = 0;
int count = 0;
vector<int>levelNums;
while(!oneQueue.empty()) {
head = oneQueue.front();
oneQueue.pop_front();
count++;
levelNums.push_back(head->val);
if (head->left != NULL) {
oneQueue.push_back(head->left);
nextLevelInternalCount++;
}
if(head->right != NULL) {
oneQueue.push_back(head->right);
nextLevelInternalCount++;
}
if (count == currentLevelInternalCount) {
vector<int> a = levelNums;
//vector<int>a(2,0);
result.push_back(a);
levelNums.clear();
count = 0;
currentLevelInternalCount = nextLevelInternalCount;
nextLevelInternalCount = 0;
}
}
return result;
}
};
