DevGod needs to write a blog entry for this problem!

var MyHashSet = function() {
    this.map={}
};

/** 
 * @param {number} key
 * @return {void}
 */
MyHashSet.prototype.add = function(key) {
    if(!this.map[key]){
        this.map[key] = true
    }
};

/** 
 * @param {number} key
 * @return {void}
 */
MyHashSet.prototype.remove = function(key) {
    if(this.map[key]){
        delete this.map[key]
    }
};

/** 
 * @param {number} key
 * @return {boolean}
 */
MyHashSet.prototype.contains = function(key) {
    if(this.map[key]){
        return true
    }else{
        return false
    }
};

/** 
 * Your MyHashSet object will be instantiated and called as such:
 * var obj = new MyHashSet()
 * obj.add(key)
 * obj.remove(key)
 * var param_3 = obj.contains(key)
 */