leetcode1302. 层数最深叶子节点的和

基本思路：bfs
但要记住入队方式为每一层节点一起入队出队的方式。

/**
 * 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:
    queue<TreeNode*> que;
    int sum = 0;
    int deepestLeavesSum(TreeNode* root) {
        que.push(root);
        while(que.size())
        {
            sum = 0;
            int n = que.size();
            for(int i = 0; i<n; i++)           //将上一层节点出队，将下一层所有节点入队
            {
                auto p = que.front();
                que.pop();
                sum += p -> val;         
                if(p -> left) que.push(p -> left);
                if(p -> right) que.push(p -> right);
            }
        }
        return sum;
    }
};
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