代碼題(7)— 二叉樹的層次遍歷
阿新 • • 發佈:2018-06-23
通過 push_back gin 節點 null node desc 二叉 for
1、102. 二叉樹的層次遍歷
給定一個二叉樹,返回其按層次遍歷的節點值。 (即逐層地,從左到右訪問所有節點)。
例如:
給定二叉樹: [3,9,20,null,null,15,7]
,
3 / 9 20 / 15 7
返回其層次遍歷結果:
[ [3], [9,20], [15,7] ]
/** * 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>> res; if(root == nullptr) return res; queue<TreeNode*> qNode; qNode.push(root); TreeNode* cur = nullptr; while(!qNode.empty()) { vector<int> temp; int num = qNode.size(); for(int i=0;i<num;++i) { cur = qNode.front(); temp.push_back(cur->val); qNode.pop(); if(cur->left != nullptr) qNode.push(cur->left);if(cur->right != nullptr) qNode.push(cur->right); }
//如果從底向上輸出,則通過插入的方式
//res.insert(res.begin(), temp); res.push_back(temp); } return res; } };
2、103. 二叉樹的鋸齒形層次遍歷
給定一個二叉樹,返回其節點值的鋸齒形層次遍歷。(即先從左往右,再從右往左進行下一層遍歷,以此類推,層與層之間交替進行)。
例如:
給定二叉樹 [3,9,20,null,null,15,7]
,
3 / 9 20 / 15 7
返回鋸齒形層次遍歷如下:
[ [3], [20,9], [15,7] ]
/** * 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>> zigzagLevelOrder(TreeNode* root) { vector<vector<int>> res; if(root == nullptr) return res; stack<TreeNode*> st1, st2; st1.push(root); while(!st1.empty() || !st2.empty()) { if(!st1.empty()) { vector<int> temp; while(!st1.empty()) { TreeNode* cur = st1.top(); temp.push_back(cur->val); st1.pop(); if(cur->left) st2.push(cur->left); if(cur->right) st2.push(cur->right); } res.push_back(temp); } if(!st2.empty()) { vector<int> temp; while(!st2.empty()) { TreeNode* cur = st2.top(); temp.push_back(cur->val); st2.pop(); if(cur->right) st1.push(cur->right); if(cur->left) st1.push(cur->left); } res.push_back(temp); } } return res; } };
代碼題(7)— 二叉樹的層次遍歷