题解链接： http://domjudge.newitd.com/public/problems/77/text

std链接：
A: 不放了
B: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148540
C: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148561
D: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148543
E: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148635
F: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148581
G: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148640
H: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148650
I: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148585
J: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148556
K: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148642
L: https://ac.nowcoder.com/acm/contest/view-submission?submissionId=47148616