题目：

题解：

bool isPerfectSquare(int num) 
{
   long long  left=0;
   long  long  right=num;
    while(left<=right)
    {
        long long mid=(left+right)/2;
        long long ans=mid*mid;
        if(ans<num)
        {
        left=mid+1;
        }
        else if(ans>num)
        {
            right=mid-1;
        }
        else
        {
        return true;
        }
    }
    return false;
}