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Balanced Binary Tree

ID: 110; easy

Solution 1 (Go)

/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func isBalanced(root *TreeNode) bool {
if root == nil {
return true
}
leftDepth := depthHelper(root.Left)
rightDepth := depthHelper(root.Right)
if abs(leftDepth - rightDepth) > 1 {
return false
}
return isBalanced(root.Left) && isBalanced(root.Right)
}
func depthHelper(root *TreeNode) int {
if root == nil {
return 0
}
return max(depthHelper(root.Left), depthHelper(root.Right)) + 1
}
func max(x, y int) int {
if x > y {
return x
}
return y
}
func abs(x int) int {
if x >= 0 {
return x
}
return -x
}

Solution 2 (Java)

/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root: The root of binary tree.
* @return: True if this Binary tree is Balanced, or false.
*/
public boolean isBalanced(TreeNode root) {
if (root == null)
return true;
int leftDepth = depthHelper(root.left);
int rightDepth = depthHelper(root.right);
if (Math.abs(leftDepth - rightDepth) > 1)
return false;
return isBalanced(root.left) && isBalanced(root.right);
}
private int depthHelper(TreeNode root) {
if (root == null)
return 0;
int left = depthHelper(root.left);
int right = depthHelper(root.right);
return Math.max(left, right) + 1;
}
}

Solution 3 (Java)

/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
private boolean balanced = true;
/**
* @param root: The root of binary tree.
* @return: True if this Binary tree is Balanced, or false.
*/
public boolean isBalanced(TreeNode root) {
depthHelper(root);
return balanced;
}
private int depthHelper(TreeNode root) {
if (root == null)
return 0;
int left = depthHelper(root.left);
int right = depthHelper(root.right);
if (Math.abs(left - right) > 1)
balanced = false;
return Math.max(left, right) + 1;
}
}

Notes

  • The refactored version of Solution 2.
  • Solution 2 should be easier to follow and understand.