方法二 自底向上
class Solution {
public boolean isBalanced(TreeNode root) {
return height(root) >= 0;
}
public int height(TreeNode root) {
if (root == null) {
return 0;
}
int leftHeight = height(root.left);
int rightHeight = height(root.right);
if (leftHeight == -1 || rightHeight == -1 || Math.abs(leftHeight - rightHeight) > 1) {
return -1;
} else {
return Math.max(leftHeight, rightHeight) + 1;
}
}
}
方法一 自顶向下
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public boolean isBalanced(TreeNode root) {
if(root == null) {
return true;
}
//先判断当前节点 然后判断左右节点
return Math.abs(height(root.left) - height(root.right)) <= 1 && isBalanced(root.left) && isBalanced(root.right);
}
public int help(TreeNode root) {
if(root == null) {
return 0;
}
int left = height(root.left);
int right = height(root.right);
return Math.max(left, right) + 1;
}
}
这个也是自底向上
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public boolean isBalanced(TreeNode root) {
if(root == null) {
return true;
}
//判断当前节点时，先判断左右节点
return isBalanced(root.left) && isBalanced(root.right) && Math.abs(help(root.left) - help(root.right)) <= 1;
}
public int help(TreeNode root) {
if(root == null) {
return 0;
}
int left = help(root.left);
int right = help(root.right);
return Math.max(left, right) + 1;
}
}