把排序数组转换为高度最小的二叉搜索树convert-sorted-array-to-binary-search-tree-with-minimal-height

[1,2,3,4,5,6,7]

4
/   \
2     6
/ \    / \
1   3  5   7

/**
* Definition of TreeNode:
* public class TreeNode {
*     public int val;
*     public TreeNode left, right;
*     public TreeNode(int val) {
*         this.val = val;
*         this.left = this.right = null;
*     }
* }
*/
public class Solution {
/**
* @param A: an integer array
* @return: a tree node
*/
public TreeNode sortedArrayToBST(int[] A) {
// write your code here
if(A.length ==0 )  return null;
return sortedToBST(A, 0, A.length-1);
}
public TreeNode sortedToBST(int[] A,int start,int end){
if (start > end)
return null;
int mid = (start+end)/2;
TreeNode root = new TreeNode(A[mid]);
root.left = sortedToBST(A,start,mid-1);
root.right  = sortedToBST(A,mid+1,end);
return root;
}
}