对称二叉树

 

 

 

 

//1.层序遍历
//2.递归，最左和最右比较
var isSymmetric = function(root) {
    var cmp = function(p1,p2){
        if( !p1 && !p2 ) return true;
        if( !p1 || !p2 ) return false;
        if( p1.val != p2.val) return false;
        return cmp(p1.left,p2.right) && cmp(p1.right,p2.left);
    }
    if(!root) return true;
    return cmp(root.left,root.right);
};