力扣-102. 二叉树的层序遍历

102. 二叉树的层序遍历

AC Code

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<int> level;
        vector<vector<int>> res;
        queue<TreeNode*> s;
        unordered_map<TreeNode*,int> r;
        if(root==NULL) return res;
        s.push(root);
        r[root]=1;
        int curLevel=1;
        while(!s.empty())
        {
            root=s.front();
            s.pop();
            int curNodeLevel=r[root];
            if(curLevel==curNodeLevel){
                level.push_back(root->val);
            }else{
                curLevel++;
                res.push_back(level);
                level.clear();
                level.push_back(root->val);
            }
            
            if(root->left!=NULL) {
                s.push(root->left);
                r[root->left]=curNodeLevel+1;
            }
            if(root->right!=NULL) {
                s.push(root->right);
                r[root->right]=curNodeLevel+1;
            }
        }
        res.push_back(level);
        return res;
    }
};