leetcode/JulyChallenge/Week1/2-BinaryTreeLevelOrderTraversalII.cpp at master · thepushkarp/leetcode · GitHub

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/**
 * 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 {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        if (root == nullptr) return {};
        vector<vector<int>> ans;
        queue<TreeNode*> q;
        q.push(root);
        while (q.empty() == false)
        {
            int nodeCount = q.size();
            vector<int> v;
            while (nodeCount > 0)
            {
                TreeNode* node = q.front();
                v.push_back(node-> val);
                q.pop();
                if (node -> left != nullptr)
                    q.push(node -> left);
                if (node -> right != nullptr)
                    q.push(node -> right);
                nodeCount--;
            }
            ans.push_back(v);
        }
        reverse(ans.begin(), ans.end());
        return ans;
    }
};