题目描述

从上往下打印出二叉树的每个节点，同层节点从左至右打印。

题解

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
        vector<int> result;
        if(root == nullptr)
            return result;
        queue1.push(root);
        while(!queue1.empty() || !queue2.empty()) {
            while(!queue1.empty()) {
                auto tmp = queue1.front();
                result.push_back(tmp->val);
                if(tmp->left != nullptr)
                    queue2.push(tmp->left);
                if(tmp->right != nullptr)
                    queue2.push(tmp->right);
                queue1.pop();
            }
            while(!queue2.empty()) {
                auto tmp = queue2.front();
                result.push_back(tmp->val);
                if(tmp->left != nullptr)
                    queue1.push(tmp->left);
                if(tmp->right != nullptr) 
                    queue1.push(tmp->right);
                queue2.pop();
            }
        }
        return result;
    }

private:
    queue<TreeNode*> queue1;
    queue<TreeNode*> queue2;
};