Leetcode题解（32）

107. Binary Tree Level Order Traversal II

题目

直接代码：

 /**
  * 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>> levelOrderBottom(TreeNode* root) {
        vector<vector<int>> res;
        vector<int> temp;
        if(NULL == root)
            return res;

        queue<TreeNode*> myQue;
        TreeNode *temp1;
        bool flag = true;
        myQue.push(root);

        while (!myQue.empty())
        {
            temp.clear();
            myQue.push(NULL);
            temp1 = myQue.front();
            myQue.pop();
            while (NULL != temp1)
            {
                temp.push_back(temp1->val);
                if(NULL != temp1->left)
                    myQue.push(temp1->left);
                if(NULL != temp1->right)
                    myQue.push(temp1->right);
                temp1 = myQue.front();
                myQue.pop();
            }

            res.push_back(temp);
        }
        reverse(res.begin(),res.end());
        return res;
     }

 };

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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：

 /**
  * 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:
     TreeNode* sortedArrayToBST(vector<int>& nums) {
         int size = nums.size();
         if( == size)
             return NULL;
         TreeNode *root = mySortedArrayToBST(nums,,size-);
         return root;
     }
     TreeNode* mySortedArrayToBST(vector<int>& nums,int start,int end)
     {
         int middle = (start+end)/;
         TreeNode *temp = new TreeNode(nums[middle]);
         if(middle == start)
             temp->left = NULL;
         else
             temp->left = mySortedArrayToBST(nums,start,middle-);

         if(middle == end)
             temp->right = NULL;
         else
             temp->right = mySortedArrayToBST(nums,middle+,end);

         return temp;
     }
 };