Is the second string a rotated version of the first string JavaScript

We are required to write a JavaScript function that takes in two strings, say str1 and str2. We are required to determine whether or not the second string is a rotated version of the first string.

For example ? If the input strings are ?

const str1 = 'abcde';
const str2 = 'cdeab';

Then the output should be true because str2 is indeed made by shifting 'ab' to the end of string in str1.

Understanding String Rotation

A string rotation means taking some characters from the beginning of a string and moving them to the end. For example, rotating "abcde" by 2 positions gives "cdeab".

Method 1: Using Concatenation Approach

The most elegant solution is to check if str2 exists as a substring in str1 + str1. This works because concatenating a string with itself contains all possible rotations.

const isRotatedConcat = (str1, str2) => {
    // Check if lengths are equal and strings are not empty
    if (str1.length !== str2.length || str1.length === 0) {
        return str1.length === str2.length;
    }
    
    // Check if str2 is a substring of str1 + str1
    return (str1 + str1).includes(str2);
};

const str1 = 'abcde';
const str2 = 'cdeab';
console.log(isRotatedConcat(str1, str2));

// Test with more examples
console.log(isRotatedConcat('hello', 'llohe')); // true
console.log(isRotatedConcat('abcd', 'bcda'));   // true
console.log(isRotatedConcat('abcd', 'bcde'));   // false

true
true
true
false

Method 2: Using Slice and Compare

This approach generates all possible rotations of str1 and checks if any matches str2.

const isRotatedSlice = (str1, str2) => {
    if (str1.length !== str2.length) {
        return false;
    }
    
    if (str1.length === 0) {
        return true;
    }
    
    for (let i = 0; i < str1.length; i++) {
        const rotated = str1.slice(i) + str1.slice(0, i);
        if (rotated === str2) {
            return true;
        }
    }
    
    return false;
};

const str1 = 'abcde';
const str2 = 'cdeab';
console.log(isRotatedSlice(str1, str2));

// Show the rotation process
console.log("Rotations of 'abcde':");
for (let i = 0; i < str1.length; i++) {
    const rotated = str1.slice(i) + str1.slice(0, i);
    console.log(`Position ${i}: ${rotated}`);
}

true
Rotations of 'abcde':
Position 0: abcde
Position 1: bcdea
Position 2: cdeab
Position 3: deabc
Position 4: eabcd

Comparison

Edge Cases

// Test edge cases
console.log("Edge cases:");
console.log(isRotatedConcat('', ''));           // true - both empty
console.log(isRotatedConcat('a', 'a'));         // true - same single char
console.log(isRotatedConcat('abc', 'ab'));      // false - different lengths
console.log(isRotatedConcat('aaa', 'aaa'));     // true - repeated chars

Edge cases:
true
true
false
true

Conclusion

The concatenation method is more efficient and cleaner for checking string rotations. It leverages the fact that all rotations of a string appear as substrings when the string is concatenated with itself.