Password Strength Checker - Problem

Given a password string, check if it meets all the strength requirements.

Requirements:

Minimum 8 characters long
Contains at least one uppercase letter (A-Z)
Contains at least one lowercase letter (a-z)
Contains at least one digit (0-9)
Contains at least one special character (!@#$%^&*)

Return true if the password is strong, false otherwise.

Input & Output

Example 1 — Strong Password

$ Input: password = "Password123@"

› Output: true

💡 Note: Length is 12 (≥8), contains uppercase 'P', lowercase letters 'assword', digits '123', and special character '@'. All requirements satisfied.

Example 2 — Too Short

$ Input: password = "Pass1@"

› Output: false

💡 Note: Length is only 6 characters, which is less than the required minimum of 8 characters.

Example 3 — Missing Special Character

$ Input: password = "Password123"

› Output: false

💡 Note: Has length ≥8, uppercase, lowercase, and digits, but missing a special character from the set !@#$%^&*.

Constraints

1 ≤ password.length ≤ 100
Password contains only ASCII characters
Special characters are limited to: !@#$%^&*

Visualization

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Asked in

M Microsoft 25 a Amazon 18 G Google 15

The key insight is to check all password requirements in a single pass rather than making multiple scans. Best approach uses boolean flags to track each requirement type while iterating once through the string. Time: O(n), Space: O(1)

Common Approaches

✓ Multiple Pass Check

⏱️ Time: O(n) Space: O(1)

This approach makes multiple passes through the password string, checking one requirement at a time. We first check length, then scan for uppercase letters, then lowercase letters, then digits, and finally special characters.

Single Pass Check

⏱️ Time: O(n) Space: O(1)

This optimized approach scans through the password only once, checking all requirements simultaneously. We use boolean flags to track which requirements have been satisfied and can return early once all are met.

Multiple Pass Check — Algorithm Steps

Step 1: Check if password length is at least 8
Step 2: Scan entire string looking for uppercase letters
Step 3: Scan entire string looking for lowercase letters
Step 4: Scan entire string looking for digits
Step 5: Scan entire string looking for special characters

Visualization

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Step-by-Step Walkthrough

Length Check

Count characters: 12 >= 8 ✓

Find Uppercase

Scan for A-Z: found 'P' ✓

Find Lowercase

Scan for a-z: found 'a' ✓

Find Digit

Scan for 0-9: found '1' ✓

Find Special

Scan for symbols: found '@' ✓

Code -

solution.c — C

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

bool solution(char* password) {
    int len = strlen(password);
    
    // Check length
    if (len < 8) {
        return false;
    }
    
    // Check for uppercase
    bool hasUpper = false;
    for (int i = 0; i < len; i++) {
        if (isupper(password[i])) {
            hasUpper = true;
            break;
        }
    }
    if (!hasUpper) return false;
    
    // Check for lowercase
    bool hasLower = false;
    for (int i = 0; i < len; i++) {
        if (islower(password[i])) {
            hasLower = true;
            break;
        }
    }
    if (!hasLower) return false;
    
    // Check for digit
    bool hasDigit = false;
    for (int i = 0; i < len; i++) {
        if (isdigit(password[i])) {
            hasDigit = true;
            break;
        }
    }
    if (!hasDigit) return false;
    
    // Check for special character
    char* specialChars = "!@#$%^&*";
    bool hasSpecial = false;
    for (int i = 0; i < len; i++) {
        if (strchr(specialChars, password[i]) != NULL) {
            hasSpecial = true;
            break;
        }
    }
    if (!hasSpecial) return false;
    
    return true;
}

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

Time & Space Complexity

Time Complexity

⏱️

O(n)

5 separate passes through string of length n, but still linear

✓ Linear Growth

Space Complexity

O(1)

Only using boolean variables to track requirements

✓ Linear Space

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Password Strength Checker - Problem

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Multiple Pass Check — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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