Convert String to Uppercase

TCS NQT Coding Easy Go Ad-Free - ₹20/mo

Write a program or function that takes a string as input and converts all lowercase alphabetic characters (a-z) to their uppercase equivalents (A-Z). Non-alphabetic characters (such as digits, symbols, and spaces) and already uppercase letters should remain unchanged.

Examples:

Input: "hello"

Output: "HELLO"

Explanation: All lowercase letters 'h', 'e', 'l', 'l', 'o' are converted to uppercase.

Input: "TcS NqT!"

Output: "TCS NQT!"

Explanation: Mixed case string: 'T' and 'S' remain uppercase, 'c' and 'q' and 't' are converted to 'C', 'Q', 'T', and '!' remains unchanged.

Input: "123abc DEF"

Output: "123ABC DEF"

Explanation: Digits '123' and space remain same, 'abc' converted to 'ABC', and 'DEF' already uppercase remains unchanged.

Constraints

1 ≤ length of string ≤ 1000 characters
String can contain any printable ASCII characters (including letters, digits, symbols, and spaces)
Conversion applies only to lowercase English letters (a-z); other characters are preserved

Editorial

Intuition:

The key insight is that lowercase English letters (a-z) have ASCII values exactly 32 greater than their uppercase counterparts (A-Z). By checking if a character is in the range 'a' to 'z', we can convert it to uppercase by subtracting 32 from its ASCII value. All other characters remain unchanged.

Approach:

Iterate through each character of the input string.
For each character, check if it is a lowercase letter (i.e., its ASCII value lies between 'a' (97) and 'z' (122)).
If it is lowercase, convert it to uppercase by subtracting 32 from its ASCII value.
If it is not a lowercase letter, leave it unchanged.
Build and return the resulting string from the processed characters.

#include <string>
using namespace std;

string convertToUpper(string s) {
    for (char &c : s) {
        if (c >= 'a' && c <= 'z') {
            c -= 32;
        }
    }
    return s;
}
public class Solution {
    public static String convertToUpper(String s) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c >= 'a' && c <= 'z') {
                sb.append((char)(c - 32));
            } else {
                sb.append(c);
            }
        }
        return sb.toString();
    }
}
def convert_to_upper(s):
    result = []
    for c in s:
        if 'a' <= c <= 'z':
            result.append(chr(ord(c) - 32))
        else:
            result.append(c)
    return ''.join(result)
function convertToUpper(s) {
    let result = '';
    for (let i = 0; i < s.length; i++) {
        let c = s[i];
        if (c >= 'a' && c <= 'z') {
            result += String.fromCharCode(c.charCodeAt(0) - 32);
        } else {
            result += c;
        }
    }
    return result;
}

Complexity Analysis:

Time Complexity: O(n), where n is the length of the input string. Each character is processed exactly once.

Space Complexity: O(n) for the output string. In languages with immutable strings (Java, Python, JavaScript), a new string is constructed. In C++, we modify a copy of the input string, which also requires O(n) space.

Notes

Your notes are automatically saved in your browser's local storage and will persist across sessions on this device.

Problem Categories