To Lower Case - Practice Coding Problems

To Lower Case - Problem

String Easy

Given a string s, your task is to transform all uppercase letters to lowercase while keeping all other characters unchanged.

This is a fundamental string manipulation problem that tests your understanding of character processing and ASCII values. You need to iterate through each character in the string and convert any uppercase letter (A-Z) to its corresponding lowercase letter (a-z).

Goal: Return a new string with all uppercase letters converted to lowercase.

Example: "Hello World!" becomes "hello world!"

Input & Output

example_1.py — Basic Mixed Case

$ Input: s = "Hello"

› Output: "hello"

💡 Note: The uppercase letters 'H' is converted to 'h', while lowercase letters remain unchanged

example_2.py — Mixed with Numbers and Symbols

$ Input: s = "Hello123World!"

› Output: "hello123world!"

💡 Note: Only uppercase letters 'H' and 'W' are converted to lowercase. Numbers and special characters remain the same

example_3.py — Already Lowercase

$ Input: s = "lovely"

› Output: "lovely"

💡 Note: Since all characters are already lowercase or non-alphabetic, the string remains unchanged

Constraints

1 ≤ s.length ≤ 100
s consists only of printable ASCII characters

Visualization

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Understanding the Visualization

Read Character

Examine each character in the input string from left to right

Check Case

Determine if the character is an uppercase letter (A-Z)

Transform

Convert uppercase letters to lowercase, keep all other characters unchanged

Build Result

Append the processed character to the result string

Key Takeaway

🎯 Key Insight: This problem teaches fundamental string manipulation - processing each character exactly once while applying a simple transformation rule. The beauty lies in its simplicity and the fact that it has a linear time solution.

Asked in

a Amazon 15 G Google 12 ⊞ Microsoft 8 Apple 5

The optimal approach is to iterate through each character once and convert uppercase letters to lowercase. While you can manually use ASCII arithmetic (adding 32 to uppercase letters), most languages provide built-in methods like toLowerCase() or lower() that handle this efficiently. The time complexity is O(n) where n is the string length.

Common Approaches

Approach	Time	Space	Notes
✓ Character-by-Character Manual Conversion	O(n)	O(n)	Check each character and manually convert using ASCII values

Character-by-Character Manual Conversion — Algorithm Steps

Iterate through each character in the string
Check if character is uppercase (ASCII 65-90)
If uppercase, convert by adding 32 to ASCII value
If not uppercase, keep character unchanged
Build result string character by character

Visualization

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Step-by-Step Walkthrough

Check Character

Examine if current character is uppercase (ASCII 65-90)

Convert or Keep

If uppercase, add 32 to ASCII value; otherwise keep unchanged

Build Result

Append converted character to result string

Code -

solution.c — C

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char* toLowerCase(char* s) {
    int len = strlen(s);
    char* result = (char*)malloc((len + 1) * sizeof(char));
    
    for (int i = 0; i < len; i++) {
        // Check if character is uppercase (A-Z)
        if (s[i] >= 'A' && s[i] <= 'Z') {
            // Convert to lowercase by adding 32
            result[i] = s[i] + 32;
        } else {
            result[i] = s[i];
        }
    }
    result[len] = '\0';
    return result;
}

int main() {
    char s[1001];
    fgets(s, sizeof(s), stdin);
    // Remove newline and quotes
    s[strcspn(s, "\n")] = 0;
    if (s[0] == '"') {
        memmove(s, s+1, strlen(s));
        s[strlen(s)-1] = '\0';
    }
    
    char* result = toLowerCase(s);
    printf("\"%s\"\n", result);
    free(result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

We visit each character exactly once, where n is the length of the string

✓ Linear Growth

Space Complexity

O(n)

We create a new string of the same length as the input

⚡ Linearithmic Space

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Smart Actions

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Character-by-Character Manual Conversion — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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