平衡二叉树

/*
 * Java Stream 方式：
 * 1. 使用一个内部类保存树的深度和是否平衡。
 * 2. 使用递归和流处理来计算树的深度和是否平衡。
 */
import java.util.stream.*;
 
public class Solution {
    public boolean isBalanced(TreeNode root) {
        return checkHeight(root).isBalanced;
    }
 
    private NodeInfo checkHeight(TreeNode node) {
        if (node == null) return new NodeInfo(0, true);
        NodeInfo leftInfo = checkHeight(node.left);
        NodeInfo rightInfo = checkHeight(node.right);
        boolean isBalanced = leftInfo.isBalanced && rightInfo.isBalanced && Math.abs(leftInfo.depth - rightInfo.depth) <= 1;
        int depth = Math.max(leftInfo.depth, rightInfo.depth) + 1;
        return new NodeInfo(depth, isBalanced);
    }
 
    private static class NodeInfo {
        int depth;
        boolean isBalanced;
 
        NodeInfo(int depth, boolean isBalanced) {
            this.depth = depth;
            this.isBalanced = isBalanced;
        }
    }
}