Same Tree

Q:
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.


A:

public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if(p == null && q == null){
            return true;
        }else if(p!= null && q == null){
            return false;
        }else if(p == null && q!= null){
            return false;
        }else{  //both p and q are not null
            if (p.val != q.val ){
                return false;
            }else{
                boolean isLeftSame = isSameTree(p.left, q.left);
                boolean isRightSame = isSameTree(p.right,q.right);
                return (isLeftSame && isRightSame);
            }
            
        }
        
    }
}

---------------------------第二遍 --------------------
思路一样，就是 没有用那么多的else if 语句。 因为，都是一个个的情况排除了。

public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if(p == null && q == null )
            return true;
        if(  ( p== null && q != null ) || (p != null && q==null))
            return false;
        // now  both are not null
        if( p.val != q.val)
            return false;
        // not both are the same value
        boolean left = isSameTree(p.left, q.left);
        boolean right = isSameTree(p.right, q.right);
        return left && right;
    }
}

Mistakes: 





Learned: