leetcode -- Same Tree

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if((p == null) && (q == null)){
            return true;
        } else if((p != null) && (q != null)){
            return cmp(p, q);
        } else {
            return false;
        }
        
    }
    
    public boolean cmp(TreeNode p, TreeNode q){
        if(p.val != q.val){
            return false;
        }
        
        TreeNode pl = p.left, pr = p.right;
        TreeNode ql = q.left, qr = q.right;
        
        if(((pl == null) && (ql != null)) || ((pl != null) && (ql == null))){
            return false;
        }
        
        if(((pr == null) && (qr != null)) || ((pr != null) && (qr == null))){
            return false;
        }
        boolean lFlag = true;
        boolean rFlag = true;
        if((pl != null) && (ql != null)){
            lFlag = cmp(pl, ql);
        }
        if((pr != null) && (qr != null)){
            rFlag = cmp(pr, qr);
        }
        return lFlag && rFlag;
    }
}