题解 | #将升序数组转化为平衡二叉搜索树#

public class Solution { public static void main(String[] args) { Solution solution = new Solution(); int[] arr = {-1,0,1,2}; TreeNode treeNode = solution.sortedArrayToBST(arr); treeNode.print(); }

public TreeNode sortedArrayToBST (int[] num) {
    // write code here
    if (num.length == 0){
        return null;
    }

   return buildTreeNode(num, 0, num.length);
}

private TreeNode buildTreeNode(int[] num, int left, int right){
    if (left >= right){
        return null;
    }
    int mid = (left + right) >> 1;
    int rootValue = num[mid];
    TreeNode treeNode = new TreeNode();
    treeNode.val = rootValue;
    treeNode.right = buildTreeNode(num, mid + 1, right);
    treeNode.left = buildTreeNode(num, left, mid);
    return treeNode;
}

}

class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null;

public void print(){
    System.out.print(this.val + " ");
    if (this.left != null){
        this.left.print();
    }
    if (this.right != null){
        this.right.print();
    }
}

}