题解 | #牛群分层排列#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
#include <vector>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return string字符串vector
     */
    vector<string> levelOrder(TreeNode* root) {
        // write code here
        if(!root) return {};
        queue<TreeNode*> cows;
        vector<string> res;
        cows.push(root);
        while (!cows.empty()) {
            int size=cows.size();
            string cs="";
            for(int i=0;i<size;i++){
                TreeNode *p=cows.front();
                cows.pop();
                if(!p) continue;
                cs += to_string(p->val);
                cows.push(p->left);
                cows.push(p->right);
            }
            if(cs!="") res.push_back(cs);
        }
        return res;
    }
};