【平衡二叉树】leetcode 110. Balanced Binary Tree

leetcode 110. Balanced Binary Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isBalanced(TreeNode root) {
        if(root==null) return true;
        int leftheight = getheight(root.left);
        int rightheight = getheight(root.right);
        if(leftheight==-1||rightheight==-1)  return false;
        if(leftheight-rightheight<=1&&leftheight-rightheight>=-1){
            return true;
        }else{
            return false;
        }
    }
    private int getheight(TreeNode root){
        if(root==null) return 0;
        int l = getheight(root.left);
        int r = getheight(root.right);
        if(l==-1||r==-1) return -1;
        else{
            if(l-r<=1&&l-r>=-1){
                return 1+(l>r?l:r);
            }else{
                return -1;
            }
        }
    }
}

稍微改动一点，这样才是优化： 1ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isBalanced(TreeNode root) {
        if(root==null) return true;
        int leftheight = getheight(root.left);
        int rightheight = getheight(root.right);
        if(leftheight==-1||rightheight==-1)  return false;
        if(leftheight-rightheight<=1&&leftheight-rightheight>=-1){
            return true;
        }else{
            return false;
        }
    }
    private int getheight(TreeNode root){
        if(root==null) return 0;
        int l = getheight(root.left);
        if(l==-1) return -1;
        int r = getheight(root.right);
        if(r==-1) return -1;
        else{
            if(l-r<=1&&l-r>=-1){
                return 1+(l>r?l:r);
            }else{
                return -1;
            }
        }
    }
}