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52 | /**
* 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 {
private:
std::queue<TreeNode*> Q;
std::unordered_map<TreeNode*, int> levelMap;
vector<vector<int>> ans;
void addIntoAns(TreeNode* node) {
if (!node)
return;
int level = levelMap[node];
if (ans.size() < level) {
ans.resize(level);
}
ans[level - 1].push_back(node->val);
}
void expand(TreeNode* node) {
if (!node)
return;
if (node->left) {
Q.push(node->left);
levelMap[node->left] = levelMap[node] + 1;
}
if (node->right) {
Q.push(node->right);
levelMap[node->right] = levelMap[node] + 1;
}
}
public:
vector<vector<int>> levelOrder(TreeNode* root) {
Q.push(root);
levelMap[root] = 1;
while(!Q.empty()) {
TreeNode* cur = Q.front();
Q.pop();
addIntoAns(cur);
expand(cur);
}
return ans;
}
};
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