leetcode — balanced-binary-tree

/**
 * Source : https://oj.leetcode.com/problems/balanced-binary-tree/
 *
 *
 * Given a binary tree, determine if it is height-balanced.
 *
 * For this problem, a height-balanced binary tree is defined as a binary tree in which
 * the depth of the two subtrees of every node never differ by more than 1.
 */
public class BalancedBinaryTree {

    public boolean isBanlanced (TreeNode root) {
        return treeDepth(root) == -1 ? false : true;
    }

    /**
     * 判断一棵二叉树是否是高度平衡二叉树
     *
     * 求出左右子树各自的总高度，如果不是则及早返回-1
     *
     * @param root
     * @return
     */
    public int treeDepth (TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftDepth = treeDepth(root.leftChild);
        if (leftDepth == -1) {
            return -1;
        }

        int rightDepth = treeDepth(root.rightChild);
        if (rightDepth == -1) {
            return -1;
        }
        if (Math.abs(leftDepth-rightDepth) > 1) {
            return -1;
        }
        return Math.max(leftDepth, rightDepth) + 1;
    }

    public TreeNode createTree (char[] treeArr) {
        TreeNode[] tree = new TreeNode[treeArr.length];
        for (int i = 0; i < treeArr.length; i++) {
            if (treeArr[i] == '#') {
                tree[i] = null;
                continue;
            }
            tree[i] = new TreeNode(treeArr[i]-'0');
        }
        int pos = 0;
        for (int i = 0; i < treeArr.length && pos < treeArr.length-1; i++) {
            if (tree[i] != null) {
                tree[i].leftChild = tree[++pos];
                if (pos < treeArr.length-1) {
                    tree[i].rightChild = tree[++pos];
                }
            }
        }
        return tree[0];
    }

    private class TreeNode {
        TreeNode leftChild;
        TreeNode rightChild;
        int value;

        public TreeNode(int value) {
            this.value = value;
        }

        public TreeNode() {

        }
    }

    public static void main(String[] args) {
        BalancedBinaryTree balancedBinaryTree = new BalancedBinaryTree();
        char[] arr0 = new char[]{'#'};
        char[] arr1 = new char[]{'3','9','2','#','#','1','7'};
        char[] arr2 = new char[]{'3','9','2','#','#','1','7','5'};
        System.out.println(balancedBinaryTree.isBanlanced(balancedBinaryTree.createTree(arr0)));
        System.out.println(balancedBinaryTree.isBanlanced(balancedBinaryTree.createTree(arr1)));
        System.out.println(balancedBinaryTree.isBanlanced(balancedBinaryTree.createTree(arr2)));
    }

}