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_3 = 0 , var_4 = var_1 ;
    while ( var_3 <= var_4 ) {
      long var_6 = var_3 + ( var_4 - var_3 ) / 2 ;
      long var_7 = var_6 * var_6 ;
      if ( var_7 == var_1 ) return true ;
      else if ( var_7 < var_1 ) var_3 = var_6 + 1 ;
      else var_4 = var_6 - 1 ;
    }
    return false ;
  }
  