Note: There is no official syllabus for ZCO vs INOI vs IOITC. Syllabus for ZCO, INOI has been determined by looking at all the concepts covered in all ZCO, INOI problems since last 5 years. All the topics covered by ZCO, INOI are also in the Basic topics section of ICO online study material. Syllabus for IOITC is same as syllabus for IOI, since the training camp is training you for IOI. There is a higher focus on the topics mentioned in the Advanced topics specifically covered in ICO online study material. :)
The below tutorials are the best tutorials on the internet for each topic. If you find better tutorials for a particular topic, please share them with everyone.
Zonal Computing Olympiad (ZCO):
Indian National Olympiad in Informatics (INOI):
International Olympiad in Informatics Training Camp (IOITC):