How to verify whether a binary tree is balanced tree?

Question

                    50                      50
                   /  \                    /  \
                  20     30              30   20
Sample Tree<---   /  \                       /  \   ----> Mirror image
               70      80                   80   70
              /  \    \                    /    /  \  
             10  40     60                60   40   10

Answer 1

A balanced binary tree is a binary tree in which the depth of the two subtrees of every node differ by 1 or less. or we can say

public static int getHeight(TreeNode root) {
    if (root == null) {
        return 0;
    }
    return Math.max(getHeight(root.left), getHeight(root.right)) + 1;
}

public static boolean isBalanced(TreeNode root) {
    if (root == null) {
        return true;
    }
    int heightDiff = getHeight(root.left) - getHeight(root.right);
    if (Math.abs(heightDiff) > 1) {
        return false;
    }
    else {
        return isBalanced(root.left) && isBalanced(root.right);
    }
}

Answer 2

A tree is said to be balanced if it height at every level is 1,0,-1. Height is calculated by subtracting the number of elements on left by number of elements on right side of node