Detect Capital

Detect Capital - Problem

String Easy

We define the usage of capitals in a word to be right when one of the following cases holds:

All letters in this word are capitals, like "USA"
All letters in this word are not capitals, like "leetcode"
Only the first letter in this word is capital, like "Google"

Given a string word, return true if the usage of capitals in it is right.

Input & Output

Example 1 — Proper Case

$ Input: word = "Google"

› Output: true

💡 Note: First letter 'G' is uppercase, remaining letters 'o', 'o', 'g', 'l', 'e' are lowercase. This matches the third valid pattern.

Example 2 — All Uppercase

$ Input: word = "USA"

› Output: true

💡 Note: All letters 'U', 'S', 'A' are uppercase. This matches the first valid pattern.

Example 3 — Invalid Mixed Case

$ Input: word = "FlaG"

› Output: false

💡 Note: Mixed case with 'F' and 'G' uppercase, 'l' and 'a' lowercase. This doesn't match any of the three valid patterns.

Constraints

1 ≤ word.length ≤ 100
word consists of lowercase and uppercase English letters

Visualization

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Asked in

G Google 15 M Microsoft 12

The key insight is that there are only three valid capitalization patterns. The optimal approach counts uppercase letters in a single pass: if count is 0 (all lower), equals length (all upper), or equals 1 with first letter uppercase (proper case), return true. Time: O(n), Space: O(1)

Common Approaches

✓ Pattern Checking

⏱️ Time: O(n) Space: O(1)

Check each of the three valid patterns: all uppercase, all lowercase, or first letter uppercase with rest lowercase. Return true if any pattern matches.

Single Pass Count

⏱️ Time: O(n) Space: O(1)

Count uppercase letters while iterating once. Based on count and first character, determine if it matches any valid pattern without multiple passes.

Pattern Checking — Algorithm Steps

Check if all characters are uppercase
Check if all characters are lowercase
Check if first is uppercase and rest are lowercase

Visualization

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Step-by-Step Walkthrough

Check All Upper

Verify if every character is uppercase

Check All Lower

Verify if every character is lowercase

Check First Upper

Verify first is upper, rest are lower

Code -

solution.c — C

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

bool solution(char* word) {
    int len = strlen(word);
    
    // Check if all uppercase
    bool allUpper = true;
    for (int i = 0; i < len; i++) {
        if (!isupper(word[i])) {
            allUpper = false;
            break;
        }
    }
    
    // Check if all lowercase
    bool allLower = true;
    for (int i = 0; i < len; i++) {
        if (!islower(word[i])) {
            allLower = false;
            break;
        }
    }
    
    // Check if first upper, rest lower
    bool firstUpperRestLower = true;
    if (len > 0) {
        if (!isupper(word[0])) {
            firstUpperRestLower = false;
        } else {
            for (int i = 1; i < len; i++) {
                if (!islower(word[i])) {
                    firstUpperRestLower = false;
                    break;
                }
            }
        }
    }
    
    return allUpper || allLower || firstUpperRestLower;
}

int main() {
    char word[1000];
    fgets(word, sizeof(word), stdin);
    word[strcspn(word, "\n")] = 0;
    bool result = solution(word);
    printf(result ? "true\n" : "false\n");
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Three separate passes through the string in worst case

✓ Linear Growth

Space Complexity

O(1)

Only using boolean variables for checks

✓ Linear Space

32.0K Views

Medium Frequency

~15 min Avg. Time

890 Likes

Ln 1, Col 1

Smart Actions

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Input & Output

Constraints

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Related Problems

Common Approaches

Pattern Checking — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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