摘要：
C. Ray Tracing C. Ray Tracing There are k sensors located in the rectangular room of size n × m meters. The i-th sensor is located at point (xi, yi). 阅读全文
摘要：
D. Dense Subsequence D. Dense Subsequence You are given a string s, consisting of lowercase English letters, and the integer m. One should choose some 阅读全文