Strings: First Steps

A string is just an ordered list of characters. Two operations start everything:

• its length — how many characters it holds.
• indexing — reach a single character by position, counting from 0. In "code", position 0 is c, position 1 is o, and the last is at index length - 1.

That zero-based counting is the number-one beginner tripwire: the last valid index is length - 1, not length. Reaching index length runs off the end.

def solve(s):
    return len(s)          # the length of the string

static long solve(String s) {
    return s.length();
}

Some problems read a single word (no spaces); others read a whole line that may contain spaces. Either way your solve receives the text as a string, and the harness prints what you return. The mental model — a string is a sequence you can measure and index by position — is the base every string problem builds on.