var isPerfectSquare = function(num) {
        let l=0
        let r=num
        while(l<=r){
            let mid=l+Math.floor((r-l)>>1)
            if(mid*mid<num){
                l=mid+1
            }else if(mid*mid>num){
                r=mid-1
            }else{
                return true
            }
        }
        return false
};