Binary Tree Zigzag Level Order Traversal 【leetcode】

题意按二叉树的深度分类输出,一行正序一行倒序,用两个栈维护。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
        vector<vector<int> > v;
        vector<int> vv;
        if(!root)return v;
        stack<TreeNode*>a,b;
        int i,j,k=1;
        a.push(root);
        
        while(!a.empty())
        {
            TreeNode* temp=a.top();
            a.pop();
            vv.push_back(temp->val);
            if(k)
            {
                if(temp->left)b.push(temp->left);
                if(temp->right)b.push(temp->right);
            }
            else
            {
                if(temp->right)b.push(temp->right);
                if(temp->left)b.push(temp->left);
            }
            
            if(a.empty())
            {
                v.push_back(vv);
                vv.clear();
                k=(k+1)&1;
                swap(a,b);
            }
        }
        return v;
    }
};


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