Leetcode 572 subtree of another tree

recursive

var isSubtree = function(root, subRoot) {
    
    return dfs(root, subRoot);
};

//  This recursion is to find the root node 
const dfs = (s, t) => {
    
    if (s === null) {
    
        return false;
    }
    //  Check the tree of the current node   perhaps   The left subtree   or   Right subtree 
    return check(s, t) || dfs(s.left, t) || dfs(s.right, t);
}

//  This recursion is to check each node of the tree 
const check = (s, t) => {
    
    if (s === null && t === null) {
    
        return true;
    }
    if (s === null || t === null || s.val !== t.val) {
    
        return false;
    }
    //  At the same time, recursively check the left subtree and the right subtree 
    return check(s.left, t.left) && check(s.right, t.right);
}

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