convertSortedArrayToBinarySearchTree.java

/**
 * Definition for binary tree
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
 TreeNode buildTree(int[] num, int begin, int end) {
 
 if(begin==end) {
 TreeNode node = new TreeNode(num[begin]);
 return node;
 } else {
 int mid = begin + (end - begin)/2;
 TreeNode node = new TreeNode(num[mid]);
 if(begin<=(mid-1)) {
 node.left = buildTree(num, begin, mid - 1);
 }
 if((mid+1)<=end) {
 node.right = buildTree(num, mid + 1, end);
 }
 return node;
 }
 
 }
 
 
 public TreeNode sortedArrayToBST(int[] num) {
 if(num==null||num.length==0) {
 return null;
 }
 return buildTree(num, 0, num.length-1);
 }
}