I will reach CM after the most recent div1+2 round, here's a list of all the algorithms I've used on my past 4 official contests where I've gained the most rating:

1832A - New Palindrome: none 205576206

1832B - Maximum Sum: sorting, prefix sums 205579825

1832C - Contrast Value: none 205584244

1832D1 - Red-Blue Operations (Easy Version): (hacked but right idea) sorting, binary search 205597153

1832E - Combinatorics Problem: prefix sums, binomial coefficients 205605946

performance rating: 1927 (~2200 if i hadn't been hacked)