leetcode || 108、Convert Sorted Array to Binary Search Tree

problem:

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

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题意:将一个递增的序列 转换成一棵 平衡查找二叉树

thinking:

(1)平衡二叉树的概念:左右子树的高度差最大不能超过1,查找二叉树的概念:左孩子<父节点<右孩子

(2)二分法递归构造二叉树

(3)模板函数解决形参类型vector<int>::iterator 太长,书写不方便

code:

class Solution {
  public:
      TreeNode *sortedArrayToBST(vector<int> &num) {
          if(num.size()==0)
              return NULL;
          return make(num.begin(),num.end());
          
      }
      template<class it>
      TreeNode *make(it first,it last)
      {
          if(first==last)
              return NULL;
          it loc = first+(last-first)/2;
          TreeNode *node = new TreeNode(*loc);
          node->left=make(first,loc);
          node->right=make(loc+1,last);
          return node;
      }
  };


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