Problems below are sorted by difficulity, hope they will rocket up your coding ability...
580C - Kefa and Park
429A - Xor-tree
277A - Learning Languages
445B - DZY Loves Chemistry
115A - Party
217A - Ice Skating
320B - Ping-Pong (Easy Version)
500B - New Year Permutation
505B - Mr. Kitayuta's Colorful Graph
161D - Distance in Tree
348B - Apple Tree
29D - Ant on the Tree
327D - Block Tower
500D - New Year Santa Network
85E - Guard Towers
453C - Little Pony and Summer Sun Celebration
If you have any recommendations feel free to mention them in the comments section.
This blog will be updated on a monthly basis.
Special thanks to MhdMohammadi, M_H_M, KMAASZRAA and X_emad_X for finding these problems.