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难度：容易
要求：
给一个排序数组（从小到大），将其转换为一棵高度最小的排序二叉树。
样例
给出数组 [1,2,3,4,5,6,7], 返回
4
/ \
2 6
/ \ / \
1 3 5 7
思路：递归
/**
* 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 == null || A.length == 0) {
return null;
}
return create(A, 0, A.length - 1);
}
public TreeNode create(int[] A, int left, int right) {
if(left == right){//处理[-1,1]的情况
return new TreeNode(A[left]);
}if (left < right) {
int mid = (left + right) >> 1;
TreeNode node = new TreeNode(A[mid]);
node.left = create(A, left, mid - 1);
node.right = create(A, mid + 1, right);
return node;
} else if (left == right) {//处理[-1,1]的情况
return new TreeNode(A[left]);
}
return null;
}
}
