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【Leetcode】Binary Tree Level Order Traversal
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,#,#,15,7}
,
3 / 9 20 / 15 7
return its level order traversal as:
[ [3], [9,20], [15,7] ]
思路:使用一个队列进行存储,同时利用两个变量来记录该层的节点个数,以及下一层的节点个数。
/** * Definition for binary tree * 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 *> lq; lq.push(root); int curlc = 1; int nextlc = 0; while(!lq.empty()) { vector<int> level; while(curlc > 0) { TreeNode * temp = lq.front(); lq.pop(); curlc--; level.push_back(temp->val); if(temp->left) { lq.push(temp->left); nextlc++; } if(temp->right) { lq.push(temp->right); nextlc++; } } curlc = nextlc; nextlc = 0; result.push_back(level); } return result; } };
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