Convert Sorted Array to Binary Search Tree With Minimal Height

Given a sorted (increasing order) array, Convert it to create a binary tree with minimal height.

Example

Given [1,2,3,4,5,6,7], return

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

分析：
这是一道非常明显的递归题。取array的中间数作为树的root，array 左边部分是左子树部分，array右边部分是右子树部分。

 /**
  * 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
      * cnblogs.com/beiyeqingteng/
      */
     public TreeNode sortedArrayToBST(int[] A) {
         if (A == null || A.length == ) return null;
         return helper(A, , A.length - );
     } 

     public TreeNode helper(int[] A, int i, int j) {
         if (i == j) {
             return new TreeNode(A[i]);
         } else if (i > j) {
             return null;
         }  else {
             int mid = i + (j - i) / ;
             TreeNode root = new TreeNode(A[mid]);
             root.left = helper(A, i, mid - );
             root.right = helper(A, mid + , j);
             return root;
         }
     }
 }

转载请注明出处：cnblogs.com/beiyeqingteng/