1、按之字形順序打印二叉樹:
請實現一個函數按照之字形打印二叉樹,即第一行按照從左到右的順序打印,第二層按照從右至左的順序打印,第三行按照從左到右的順序打印,其他行以此類推。
用兩個棧
/*
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
TreeNode(int x) :
val(x), left(NULL), right(NULL) {
}
};
*/
class Solution {
public:
vector<vector<int> > Print(TreeNode* pRoot) {
vector<vector<int> > res;
if(pRoot==NULL)
return res;
stack<TreeNode*> s1;
stack<TreeNode*> s2;
vector<int> levelNodes;
s1.push(pRoot);
while(!s1.empty()||!s2.empty()){
while(!s1.empty()){
TreeNode* tmp1=s1.top();
if(tmp1->left!=NULL) s2.push(tmp1->left);
if(tmp1->right!=NULL) s2.push(tmp1->right);
levelNodes.push_back(tmp1->val);
s1.pop();
}
if(!levelNodes.empty()){
res.push_back(levelNodes);
levelNodes.clear();
}
while(!s2.empty()){
TreeNode* tmp2=s2.top();
if(tmp2->right!=NULL) s1.push(tmp2->right);
if(tmp2->left!=NULL) s1.push(tmp2->left);
levelNodes.push_back(tmp2->val);
s2.pop();
}
if(!levelNodes.empty()){
res.push_back(levelNodes);
levelNodes.clear();
}
}
return res;
}
};
2、把二叉樹打印成多行:
從上到下按層打印二叉樹,同一層結點從左至右輸出。每一層輸出一行。
/*
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
TreeNode(int x) :
val(x), left(NULL), right(NULL) {
}
};
*/
class Solution {
public:
vector<vector<int> > Print(TreeNode* pRoot) {
vector<vector<int> > res;
queue<TreeNode*> q;
if(pRoot)
q.push(pRoot);
int n=q.size();
//n獲取隊列的大小,不用額外的變量記錄每一層的個數
while(n){
vector<int> levelNodes;
while(n--){
TreeNode* tmp=q.front();
if(tmp->left)
q.push(tmp->left);
if(tmp->right)
q.push(tmp->right);
levelNodes.push_back(tmp->val);
q.pop();
}
res.push_back(levelNodes);
n=q.size();
}
return res;
}
};