leetCode(41):Convert Sorted Array to Binary Search Tree

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

取中间的结点作为根结点即平衡二叉树

/**
 * 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* ArrayToBst(vector<int>& nums, int start, int end)
    {
    	if (start == end)
    		return NULL;
    	int mid = (start + end) / 2;
    	TreeNode* root = new TreeNode(nums[mid]);
    	root->left = ArrayToBst(nums, start, mid);//左右子树直接递归
    	root->right = ArrayToBst(nums, mid+1, end);
    	return root;
    }

    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return ArrayToBst(nums, 0, nums.size());
    }
};

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