按之字形顺序打印二叉树

题目描述

请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推

 

/*
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>>ret;
        if(!pRoot)	return ret;
        stack<TreeNode*> stack[2];
        int cur=0;
        int next=1;
        stack[cur].push(pRoot);
        vector<int> curVec;
        while(!stack[0].empty() || !stack[1].empty()) {
            TreeNode * pNode=stack[cur].top();
            curVec.push_back(pNode->val);
            stack[cur].pop();
            if(cur==0) {
                if(pNode->left)
                    stack[next].push(pNode->left);
                if(pNode->right)
                    stack[next].push(pNode->right);
            }
            else {
                if(pNode->right)
                    stack[next].push(pNode->right);
                if(pNode->left)
                    stack[next].push(pNode->left);
            }
            
            if(stack[cur].empty()) {
                ret.push_back(curVec);
                curVec.clear();
                cur=1-cur;
                next=1-next;
            }
        }
        return ret;
    }
    
};

　　

按之字形顺序打印二叉树

class Solution {
public:
     vector<vector<int> > Print(TreeNode* pRoot) {
	    vector<vector<int> > result;
        if (pRoot == NULL)
            return result;
        stack<TreeNode*> stk1, stk2;
        stk1.push(pRoot); // stk1 存储奇数层；stk2 存储偶数层
        while (!stk1.empty() || !stk2.empty()) {
            vector<int> level_vec;
            if (!stk1.empty()) {
                while (!stk1.empty()) {
                    TreeNode* pTop = stk1.top();
                    level_vec.push_back(pTop->val);
                    if (pTop->left != NULL) // 入栈先左后右，出栈时从右向左（偶数层）
                        stk2.push(pTop->left);
                    if (pTop->right != NULL)
                        stk2.push(pTop->right);
                    stk1.pop();
                }
            } else {
                while (!stk2.empty()) {
                    TreeNode* pTop = stk2.top();
                    level_vec.push_back(pTop->val);
                    if (pTop->right != NULL) // 入栈先右后左，出栈时先左后右（奇数层）
                        stk1.push(pTop->right);
                    if (pTop->left != NULL)
                        stk1.push(pTop->left);
                    stk2.pop();                   
                }
            }
            result.push_back(level_vec);
        }
        return result;
     }
};

　　

层次遍历加上判断奇偶改变方向就行

/*
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;
        if(pRoot==NULL)	return res;
        queue<TreeNode*> que;
        que.push(pRoot);
        bool even=false;
        while(!que.empty()) {
            vector<int> vec;
            const int size=que.size();
            for(int i=0;i<size;i++) {
                TreeNode * tmp=que.front();
                que.pop();
                vec.push_back(tmp->val);
                if(tmp->left !=NULL)	que.push(tmp->left);
                if(tmp->right!=NULL)	que.push(tmp->right);
	        }
            if(even)
                reverse(vec.begin(),vec.end());
            res.push_back(vec);
            even=!even;
        }
        return res;
        
        
    }
    
};