To Lower Case - Practice Coding Problems

To Lower Case - Problem

String Easy

Given a string s, return the string after replacing every uppercase letter with the same lowercase letter.

Input & Output

Example 1 — Mixed Case

$ Input: s = "Hello"

› Output: "hello"

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

Example 2 — All Uppercase

$ Input: s = "HERE"

› Output: "here"

💡 Note: All uppercase letters H, E, R, E are converted to their lowercase equivalents h, e, r, e.

Example 3 — Already Lowercase

$ Input: s = "lovely"

› Output: "lovely"

💡 Note: String is already lowercase, so no changes are made.

Constraints

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

Visualization

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Understanding the Visualization

Input

String with uppercase and lowercase letters

Process

Convert all uppercase letters to lowercase

Output

String with all letters in lowercase

Key Takeaway

🎯 Key Insight: Use built-in string methods for simple and efficient case conversion

Asked in

G Google 15 a Amazon 12 M Microsoft 8

The key insight is that uppercase letters have ASCII values exactly 32 less than their lowercase counterparts. Best approach is using built-in toLowerCase() function. Time: O(n), Space: O(n)

Common Approaches

Approach	Time	Space	Notes
✓ Character-by-Character Check	O(n)	O(n)	Manually check each character and convert uppercase to lowercase using ASCII values
Built-in Function	O(n)	O(n)	Use language's built-in toLowerCase() or equivalent function

Character-by-Character Check — Algorithm Steps

Iterate through each character in the string
Check if character is uppercase (A-Z)
If uppercase, convert to lowercase by adding 32
Build result string with converted characters

Visualization

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Step-by-Step Walkthrough

Check Character

Examine if character is uppercase

Convert

Add 32 to ASCII value if uppercase

Append

Add converted character to result

Code -

solution.c — C

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

char* solution(char* s) {
    int len = strlen(s);
    char* result = (char*)malloc((len + 1) * sizeof(char));
    
    for (int i = 0; i < len; i++) {
        if (s[i] >= 'A' && s[i] <= 'Z') {
            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);
    s[strcspn(s, "\n")] = 0;
    
    char* result = solution(s);
    printf("%s\n", result);
    free(result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single pass through string of length n

✓ Linear Growth

Space Complexity

O(n)

New string to store the result

⚡ Linearithmic Space

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Medium Frequency

~5 min Avg. Time

956 Likes

Ln 1, Col 1

Smart Actions

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Character-by-Character Check — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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