Leetcode 108. Convert Sorted Array to Binary Search Tree

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

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

method 1

本题只要熟悉概念就会做，构造的二叉树要求是AVL树，那么我们可以使用分治法，取中间的数作为根节点，然后对左右两边采取同样的操作

TreeNode* helper(vector<int>& nums, int low, int high){
	if (low > high) return NULL;

	int mid = (low + high) / 2;
	TreeNode* root = new TreeNode(nums[mid]);
	root->left = helper(nums, low, mid - 1);
	root->right = helper(nums, mid + 1, high);
	return root;
}

TreeNode* sortedArrayToBST(vector<int>& nums) {
	if (nums.size() == 0)
		return NULL;

	return helper(nums, 0, nums.size() - 1);
}

summary

1. 大问题可以化为小问题–> 分治法