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  • LeetCode

    题目:

    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.

    思路:

    1) 计算结点的高度,但这个有重复计算

    package tree;
    
    public class BalancedBinaryTree {
        
        public boolean isBalanced(TreeNode root) {
            if (root == null) return true;
            int leftHeight = height(root.left);
            int rightHeight = height(root.right);
            return Math.abs(leftHeight - rightHeight) <= 1 &&
                    isBalanced(root.left) && isBalanced(root.right);
        }
        
        private int height(TreeNode root) {
            if (root == null) return 0;
            return Math.max(1 + height(root.left), 1 + height(root.right));
        }
        
    }

    2) 不进行重复计算,但需要new 对象,反而也花时间

    package tree;
    
    public class BalancedBinaryTree {
        
        class Entry{
            public int height;
            public boolean balanced;
        }
        
        public boolean isBalanced(TreeNode root) {
            return checkTree(root).balanced;
        }
        
        private Entry checkTree(TreeNode root) {
            Entry entry = new Entry();
            if (root == null) {
                entry.height = 0;
                entry.balanced = true;
            } else {
                Entry left = checkTree(root.left);
                Entry right = checkTree(root.right);
                entry.height = Math.max(left.height, right.height) + 1;
                entry.balanced = Math.abs(left.height - right.height) <= 1 && left.balanced && right.balanced;
            }
            return entry;
        }
        
    }
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  • 原文地址:https://www.cnblogs.com/null00/p/5118171.html
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