Briefly tell what the main task of a hash function is and how it is used in programming?

A hash function is a function that takes input data (such as a string or object) and returns a fixed-size value — a hash (usually a number).

The main task of a hash function is to quickly and unambiguously transform data into a compact representation, so that it can be efficiently compared, searched, or stored.

In programming, hash functions are used:

• In hash tables (e.g., dictionaries) to quickly find elements by key.
• To verify data integrity (checksums).
• In cryptography for creating digital signatures and passwords.

Example in Dart (Flutter):

int simpleHash(String s) {
  int hash = 0;
  for (int i = 0; i < s.length; i++) {
    hash = (hash * 31 + s.codeUnitAt(i)) & 0x7fffffff;
  }
  return hash;
}