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
        // 广度优先搜索
        vector<string> ans;
        if(!root)
            return ans;

        queue<TreeNode*> q;
        q.push(root);

        while(!q.empty())
        {
            int len = q.size();
            string str = "";
            for(int i=0; i<len; ++i)
            {
                TreeNode* t = q.front();
                q.pop();
                str += to_string(t->val);
                
                if(t->left)
                    q.push(t->left);
                if(t->right)
                    q.push(t->right);
            }

            ans.emplace_back(str);
        }

        return ans;
    }
};