Day of Week Namer - Problem

Conditions Switch/Match Easy

Given a number between 1 and 7 (inclusive), return the corresponding day of the week name.

Mapping:

1 → "Monday"
2 → "Tuesday"
3 → "Wednesday"
4 → "Thursday"
5 → "Friday"
6 → "Saturday"
7 → "Sunday"

For any input outside the range 1-7, return "Invalid".

Note: This problem focuses on conditional logic and input validation.

Input & Output

Example 1 — Valid Weekday

$ Input: dayNumber = 3

› Output: Wednesday

💡 Note: Input 3 corresponds to Wednesday in the week mapping (1=Monday, 2=Tuesday, 3=Wednesday, etc.)

Example 2 — Weekend Day

$ Input: dayNumber = 7

› Output: Sunday

💡 Note: Input 7 corresponds to Sunday, the last day in our 1-7 mapping system

Example 3 — Invalid Input

$ Input: dayNumber = 8

› Output: Invalid

💡 Note: Input 8 is outside the valid range of 1-7, so we return 'Invalid' to handle the error gracefully

Constraints

Input will be an integer
Valid range is 1 ≤ dayNumber ≤ 7
Invalid inputs should return "Invalid"

Visualization

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Asked in

M Microsoft 15 I IBM 12 O Oracle 8

The key insight is to use direct mapping instead of sequential comparisons. The best approach uses array lookup or switch statements for O(1) time complexity. Time: O(1), Space: O(1)

Common Approaches

✓ Array/Map Lookup

⏱️ Time: O(1) Space: O(1)

Store day names in an array or hash map and use the input number as a direct index or key for instant lookup.

If-Else Chain

⏱️ Time: O(1) Space: O(1)

Check each possible day number (1-7) using sequential if-else conditions. For invalid inputs, return 'Invalid' as the default case.

Switch Statement

⏱️ Time: O(1) Space: O(1)

Use a switch statement to match the day number directly to its corresponding day name. More readable and efficient than if-else chains.

Array/Map Lookup — Algorithm Steps

Create array/map with day names
Validate input is in range 1-7
Use input as index/key for direct lookup
Return the corresponding day name

Visualization

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Step-by-Step Walkthrough

Array Setup

Pre-populated array with day names at indices 1-7

Direct Access

Use input number as array index for O(1) lookup

Return Result

Return day name directly from array position

Code -

solution.c — C

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

char* solution(int dayNumber) {
    static char result[20];
    // Array of day names (index 0 unused)
    char* days[] = {"", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
    
    if (dayNumber >= 1 && dayNumber <= 7) {
        strcpy(result, days[dayNumber]);
    } else {
        strcpy(result, "Invalid");
    }
    return result;
}

int main() {
    int dayNumber;
    scanf("%d", &dayNumber);
    char* result = solution(dayNumber);
    printf("%s\n", result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Direct array/hash map access takes constant time

✓ Linear Growth

Space Complexity

O(1)

Fixed-size array of 7 day names, constant space

✓ Linear Space

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Day of Week Namer - Problem

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Array/Map Lookup — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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