leetcode-102-二叉树的层次遍历

class Solution {

public:

    vector<vector<int>> levelOrder(TreeNode* root) {

        vector<vector<int>> res = {};

        TreeNode* curNode = root;

        queue<pair<TreeNode*, int>> helper;

        if (!root) return res;

        helper.push(make_pair(curNode, 0));

        while(!helper.empty()){

            curNode = helper.front().first;

            int i = helper.front().second;

            helper.pop();

            if (i >= res.size()) res.push_back( vector<int>() );

            res[i].push_back(curNode->val);

            if (curNode->left) helper.push(make_pair(curNode->left, i+1));

            if (curNode->right) helper.push(make_pair(curNode->right, i+1));

        }

        return res;

    }

};