Count Letters, Digits, Spaces and Other Characters

Easy10 min

Topics

BasicsStrings

Companies

TCSInfosysWipro

Given a string text, return [letters, digits, spaces, others]: how many characters are English letters, how many are digits, how many are spaces, and how many are anything else. Behind the scenes every character is a number — its character code. Letters and digits occupy consecutive ranges of codes, which is what makes simple range checks work. Built-in tests like isalpha wrap those checks in readable names.

Test Case 1:

Input:text = "Room 42!"

Output:[4, 2, 1, 1]

Explanation:R, o, o, m are letters; 4 and 2 are digits; one space; "!" is something else.

Test Case 2:

Input:text = "abc"

Output:[3, 0, 0, 0]

Explanation:Only letters.

Constraints

◆1 ≤ text.length ≤ 200
◆text contains printable ASCII characters

Try the Dry Run

Mode

Approach

Approach & Solutions

Compare Character RangesGood

Characters are stored as numbers, and the codes for 'a'–'z', 'A'–'Z' and '0'–'9' are each consecutive. So a character is a letter if it lies in one of the two letter ranges, a digit if it lies in the digit range, a space if it equals ' ', and anything else otherwise.

TimeO(n)

SpaceO(1)

Java

Try it out

class Solution {
    public int[] classifyCharacters(String text) {
        int letters = 0, digits = 0, spaces = 0, others = 0;
        for (char ch : text.toCharArray()) {
            if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) {
                letters++;
            } else if (ch >= '0' && ch <= '9') {
                digits++;
            } else if (ch == ' ') {
                spaces++;
            } else {
                others++;
            }
        }
        return new int[] {letters, digits, spaces, others};
    }
}

Built-in Character TestsOptimal

Use the ready-made tests: Character.isLetter and isDigit in Java, isalpha and isdigit in Python, C and C++, and small regular expressions in JavaScript. They read better than raw ranges and say exactly what is being checked.