leetcode Day1

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从零开始Leetcode – Day 1

Symmetric Tree

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var isSymmetric = function(root) {
	if(root === null){
		return true;
	}else{
		return helper(root.left , root.right);
	}
};


function helper(p , q){
	if( p === null && q ===null){
         return true;
    }     
    if( p === null || q ===null){
    	return false;
    }
    if( p.val != q.val){
    	return false;
    }else{
    	return helper(p.left, q.right) && helper(p.right , q.left);
    }
}

Same Tree

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var isSameTree = function(p, q) {
    if( p === null && q === null){
        return true;
    }
    if( p !== null || q !== null ){
        return false;
    }
    if( p.val != q.val){
        return false;
    }
    return isSameTree( p.left , q.left) && isSameTree( p.right, q.right);
};

Maximum Depth of Binary Tree

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var maxDepth = function(root) {
    if(root === null){
        return 0;
    }
    return Math.max(maxDepth(root.left) , maxDepth(root.right)) + 1;
};

Balanced Binary Tree

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var isBalanced = function(root) {
    if (root === null) {
        return true;
    }
    var leftDepth = maxDepth(root.left);
    var rightDepth = maxDepth(root.right);

    if (Math.abs(leftDepth - rightDepth) <= 1) {
        return isBalanced(root.left) && isBalanced(root.right);
    } else {
        return false;
    }
};

var maxDepth = function (root) {
    if (root === null) {
        return 0;
    }
    return Math.max(maxDepth(root.left) ,maxDepth(root.right)) + 1;
};