【LeetCode】

標籤：tree

題目

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.

解答

判斷二叉樹是否是平衡二叉樹。利用遞迴法算樹的深度，判斷左右子樹深度差是否大於1，若大於則返回false，否則遞迴調用判斷左右子樹是否同時滿足平衡的條件。代碼如下：

public class Solution {    public boolean isBalanced(TreeNode root) {        if(root==null){            return true;        }        // 如果左子樹和右子樹高度相差大於1，則非平衡二叉樹        if(Math.abs(getDepthRec(root.left)-getDepthRec(root.right))>1){            return false;        }        // 遞迴判斷左子樹和右子樹是否為平衡二叉樹          return isBalanced(root.left)&&isBalanced(root.right);    }    //a.若二叉樹為空白，深度為0;b.若二叉樹不為空白，深度=max(左子樹深度，右子樹深度)+1    private int getDepthRec(TreeNode root){        if(root==null){            return 0;        }        int leftDepth=getDepthRec(root.left);        int rightDepth=getDepthRec(root.right);        return Math.max(leftDepth,rightDepth)+1;    }}

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