LintCode 70 二叉树的层次遍历 II

题目:levelOrderBottom

要求:

样例:

给出一棵二叉树 {3,9,20,#,#,15,7},

3
/ \
9  20
/  \
15   7
按照从下往上的层次遍历为：

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

算法要求:

解题思路:

算法如下:

int getSize(TreeNode *root) {
if (root == NULL) {
return 1;
}
return getSize(root->left) + getSize(root->right);
}
vector<vector<int> > levelOrderBottom(TreeNode *root) {
// write your code here
vector<vector<int> > vec;
if (root == NULL) {
return vec;
}
int size = getSize(root) - 1;
queue<TreeNode*> que;
que.push(root);
vector<int> *v = new vector<int>();
int n = 1;
int i = 0;
int j = 0;

4000
while (!que.empty() && j < size) {
TreeNode *now = que.front();
que.pop();
i++;
if (now) {
v->push_back(now->val);
j++;
}
if (i >= n) {
i = 0;
n *= 2;
if (!v->empty()) {
vec.push_back(*v);
v = new vector<int>();
}
}
if (now) {
que.push(now->left);
que.push(now->right);
} else{
que.push(NULL);
que.push(NULL);
}
}
if (!v->empty()) {
vec.push_back(*v);
}
vector<vector<int> > vec2;
size = vec.size();
for (int i = 0; i < size; i++) {
vec2.push_back(vec[size - i - 1]);
}
return vec2;
}