LeetCode 110. Balanced Binary Tree 遞歸求解

110. Balanced Binary Tree

My SubmissionsQuestionTotal Accepted:97926Total Submissions:292400Difficulty:Easy

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 ofeverynode never differ by more than 1.

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判斷一棵樹是否是平衡二叉樹。BST的遞歸定義：當一棵樹的左右兩棵子樹的高度只差不超過1，那麼該樹是平衡二叉樹。

用後根遍歷求解。先計算兩棵子樹的高度差。

我的AC代碼

public class BalancedBinaryTree {
	static boolean ok = true;
	
	public static void main(String[] args) {
		TreeNode n1 = new TreeNode(1);
		TreeNode n2 = new TreeNode(2);
		n1.left = n2;
		System.out.println(isBalanced(n1));
	}

	public static boolean isBalanced(TreeNode root) {
        ok = true;
        dfs(root);
        return ok;
    }
	
	public static int dfs(TreeNode root) {
		if(root == null || !ok) return 0;
		int ha = dfs(root.left);
		int hb = dfs(root.right);
		
		if(Math.abs(ha - hb) > 1) ok = false;
		return Math.max(ha, hb) + 1;
	}
}