Queue template code

For the problem of binary tree , Template code implemented in queue mode

With a sword finger offerII 045. The lowest left value of a binary tree is an example ：

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode() : val(0), left(nullptr), right(nullptr) {} * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {} * TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {} * }; */
class Solution {
    
public:
    int findBottomLeftValue(TreeNode* root) {
    
        queue<TreeNode*> tree;// Template statement 1
        tree.push(root);// Template statement 2
        vector<int> row;
        while(!tree.empty()){
    
            row.clear();
            for(int i = tree.size();i>0;i--){
    // Template statement 3
                TreeNode* tmp = tree.front();// Template statement 4
                row.emplace_back(tmp->val);
                if(tmp->left!=nullptr) tree.push(tmp->left);// Template statement 5
                if(tmp->right!=nullptr) tree.push(tmp->right);// Template statement 6
                tree.pop();// Template statement 7
            }
        }
        return row[0];
    }
};

This is mainly aimed at the problem of binary tree , We use sequence traversal to achieve the corresponding subject requirements .
Something to be aware of ：

• consider root Empty situation ;
• Consider the case where the queue is empty ;
• The number of each layer of the tree can be used as a queue queue.size() To express , Because every time the root node is out of the queue , Therefore, the elements of a row are always stored in the queue .