210401 TIL

1.SQL in goormedu

symmetric pairs by hackerrank

SELECT f1.x, f1.y
FROM  functions as f1
     INNER JOIN functions as f2 ON f1.x = f2.y AND f1.y = f2.x (two join conditions make sense.)
WHERE f1.x < f1.y -- this is point

UNION

SELECT x, y
FROM functions
WHERE x = y
GROUP BY x, y  (‘GROUP BY’ works even if we input two columns at the same time.)
HAVING count(*) = 2
ORDER BY x  (‘ORDER BY’ can be used at the last sentence of UNION query)

output

 

 

2.English

<speaking review>

It looks like they didn’t know what real camping is

They didn’t seem to expect what could happen if they are on the way to the campsite

additionally/in addition to/moreover/furthermore, they gave their food to a bear (also is not accepted)

<reading - cracking the tech career>

[bookmark]

P44

“At a start-up, office managers do everything under the sun.” Kwok explains. “As the company grows, you can begin to specialize in an area like HR. Couple that with an additional night course or two in HR, and all of a sudden you’re the perfect candidate for a full-time HR-position.”

 

3.algorithm

mathmatics

def stoi(s, n):
ret = 0
l = len(s)

for i in range(l): ret += int(s[i] * n**(l-i-1)
return ret


*easier way

1 * 10 **2 + 2 * 10 ** 1 + 3 * 10 **0
-> 8times

(((0 * 10 +1) * 10) + 2) * 10 + 3
-> 6times