107. Binary Tree Level Order Traversal II

题目

直接代码：

1 /** 2  * Definition for a binary tree node. 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     vector
     
      
       > levelOrderBottom(TreeNode* root) {13        vector
       
        
         > res;14        vector
         
           temp;15        if(NULL == root)16            return res;17 18        queue
          
            myQue;19 TreeNode *temp1;20 bool flag = true;21 myQue.push(root);22 23 while (!myQue.empty())24 {25 temp.clear();26 myQue.push(NULL);27 temp1 = myQue.front();28 myQue.pop();29 while (NULL != temp1)30 {31 temp.push_back(temp1->val);32 if(NULL != temp1->left)33 myQue.push(temp1->left);34 if(NULL != temp1->right)35 myQue.push(temp1->right);36 temp1 = myQue.front();37 myQue.pop();38 }39 40 41 res.push_back(temp);42 }43 reverse(res.begin(),res.end());44 return res;45 }46 47 };
          
         
        
       
      
     

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108. Convert Sorted Array to Binary Search Tree

题目

分析：

讲一个排好序的数组，构造成平衡二叉树，并且是二叉搜索树，其基本思想是折半（二分）法。

代码如下：

1 /** 2  * Definition for a binary tree node. 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     TreeNode* sortedArrayToBST(vector
     
      & nums) {13         int size = nums.size();14         if(0 == size)15             return NULL;16         TreeNode *root = mySortedArrayToBST(nums,0,size-1);17         return root;18     }19     TreeNode* mySortedArrayToBST(vector
      
       & nums,int start,int end)20     {21         int middle = (start+end)/2;22         TreeNode *temp = new TreeNode(nums[middle]);23         if(middle == start)24             temp->left = NULL;25         else26             temp->left = mySortedArrayToBST(nums,start,middle-1);27         28         if(middle == end)29             temp->right = NULL;30         else31             temp->right = mySortedArrayToBST(nums,middle+1,end);32         33         return temp;34     }35 };