LeetCode-M-Binary Tree Level Order Traversal
2017-04-22 22:42
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题意
Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).For example:
Given binary tree [3,9,20,null,null,15,7],
3 / \ 9 20 / \ 15 7
return its level order traversal as:
[ [3], [9,20], [15,7] ]
解法
利用队列,层次遍历实现
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: vector<vector<int>> levelOrder(TreeNode* root) { vector<vector<int>> result; if(root == NULL) return result; queue<TreeNode*> tq; tq.push(root); tq.push(NULL); while(!tq.empty() && tq.front() != NULL){ vector<int> sr; while(tq.front() != NULL){ TreeNode* node = tq.front(); tq.pop(); sr.push_back(node->val); if(node->left != NULL) tq.push(node->left); if(node->right != NULL) tq.push(node->right); } tq.push(NULL); result.push_back(sr); tq.pop(); } return result; } };
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