comefrom: <awangdev>367. Valid Perfect Square_1.java
code: public boolean isPerfectSquare(int num) {
          long start = 0, end = num;
          while (start <= end) {
              long mid = start + (end - start) / 2;
              long sqrt = mid * mid;
              if (sqrt == num) return true;
              else if (sqrt < num) start = mid + 1;
              else end = mid - 1;
          }
          return false;
      }
masked: public boolean var_0 ( int var_1 ) {
    long var_2 = 0 , var_3 = var_1 ;
    while ( var_2 <= var_3 ) {
      long var_4 = var_2 + ( var_3 - var_2 ) / 2 ;
      long var_5 = var_4 * var_4 ;
      if ( var_5 == var_1 ) return true ;
      else if ( var_5 < var_1 ) var_2 = var_4 + 1 ;
      else var_3 = var_4 - 1 ;
    }
    return false ;
  }
  