1&0 : Academy
Stack : https://www.acmicpc.net/problem/10828
ant : http://codeup.kr/JudgeOnline/problem.php?id=1099
cake : http://codeup.kr/JudgeOnline/problem.php?id=2628
chess : http://codeup.kr/JudgeOnline/problem.php?id=1514
gitf : http://codeup.kr/JudgeOnline/problem.php?id=4066
tie : http://codeup.kr/JudgeOnline/problem.php?id=4862
ACM : https://www.acmicpc.net/problem/10250
ball : https://www.acmicpc.net/problem/1547
sort -> sort(0&1) : https://www.acmicpc.net/problem/1181
math_homework : https://www.acmicpc.net/problem/2870
phone : https://www.acmicpc.net/problem/5052
serial_num : https://www.acmicpc.net/problem/1431