"Sword refers to offer" prints a binary tree from top down, and the sword refers to offer rebuilding a binary tree.

"Sword refers to offer" prints a binary tree from top down, and the sword refers to offer rebuilding a binary tree.

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Question link: http://www.nowcoder.com/practice/7fe2212963db4790b57431d9ed259701? Rp = 2 & ru =/ta/coding-interviews & qru =/ta/coding-interviews/question-ranking

Description
Each node of the binary tree is printed from top to bottom, and the nodes at the same layer are printed from left to right.

Ideas
This is an obvious search question with a high degree of breadth. Starting from the root node, we first store its subnodes in the queue in the left-to-right order, according to the features of the first-in-first-out queue, each time the nodes in the pop-up queue arrive at the next layer after processing the same layer, this meets the requirements of the question.

/*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> ans;if(root==nullptr) return ans;queue<TreeNode*> Q;Q.push(root);while(!Q.empty()){TreeNode *now = Q.front();Q.pop();ans.push_back(now->val);if(now->left)Q.push(now->left);if(now->right)Q.push(now->right);}return ans;}};

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