Question

how did sutta pitaka reconstruct

Answer 1

The Sutta Pitaka is the second of the three divisions of the Tripitaka or Pali Canon, the Pali collection of Buddhist writings of Theravada Buddhism. The Sutta Pitaka contains more than 10,000 suttas (teachings) attributed to the Buddha or his close companions.
The scriptures tell how the First Council held shortly after the Buddha's death collected together the discipline (vinaya), and the dharma in five collections. Tradition holds that little was added to the Canon after this. Scholars are more skeptical, but differ in their degrees of skepticism. Richard Gombrich thinks most of the first four nikayas (see below) go back to the Buddha, in content but not in form. The late Professor Hirakawa Akira saysthat the First Council collected only short prose passages or verses expressing important doctrines, and that these were expanded into full length suttas over the next century.