Javascript Program to Modify a string by performing given shift operations

Given a string S containing lowercase English alphabets, and a matrix shift[][] consisting of pairs of the form{direction, amount}, where the direction can be 0 (for left shift) or 1 (for right shift) and the amount is the number of indices by which the string S is required to be shifted. The task is to return the modified string that can be obtained after performing the given operations.
Note: A left shift by 1 refers to removing the first character of S and append it to the end. Similarly, a right shift by 1 refers to removing the last character of S and insert at the beginning.

Examples

Input: S = "abc", shift[][] = {{0, 1}, {1, 2}}
Output: cab
Explanation: 
[0, 1] refers to shifting  S[0] to the left by 1. Therefore, the string S modifies from "abc" to "bca".
[1, 2] refers to shifting  S[0] to the right by 1. Therefore, the string S modifies from "bca"to "cab".

Input: S = "abcdefg", shift[][] = { {1, 1}, {1, 1}, {0, 2}, {1, 3} }
Output: efgabcd
Explanation:  
[1, 1] refers to shifting S[0] to the right by 1. Therefore, the string S modifies from "abcdefg" to "gabcdef".
[1, 1] refers to shifting S[0] to the right by 1. Therefore, the string S modifies from "gabcdef" to "fgabcde".
[0, 2] refers to shifting S[0] to the left by 2. Therefore, the string S modifies from "fgabcde" to "abcdefg".
[1, 3] refers to shifting S[0] to the right by 3. Therefore, the string S modifies from "abcdefg" to "efgabcd".

Naive Approach: The simplest approach to solve the problem is to traverse the matrix shift[][] and shift S[0] by amount number of indices in the specified direction. After completing all shift operations, print the final string obtained.
Time Complexity: O(N²)
Auxiliary space: O(N)

Efficient Approach: To optimize the above approach, follow the steps below:

• Initialize a variable, say val, to store the effective shifts.
• Traverse the matrix shift[][] and perform the following operations on every i^th row:
• If shift[i][0] = 0 (left shift), then decrease val by -shift[i][1].
• Otherwise (left shift), increase val by shift[i][1].
• Update val =  val % len (for further optimizing the effective shifts).
• Initialize a string, result = "", to store the modified string.
• Now, check if val > 0. If found to be true, then perform the right rotation on the string by val.
• Otherwise, perform left rotation of the string by |val| amount.
• Print the result.

Below is the implementation of the above approach:

<script>

// Javascript implementation
// of above approach

// Function to find the string obtained
// after performing given shift operations
function stringShift(s, shift)
{

    var val = 0;

    for (var i = 0; i < shift.length; ++i)

        // If shift[i][0] = 0, then left shift
        // Otherwise, right shift
        val += shift[i][0] == 0
                   ? -shift[i][1]
                   : shift[i][1];

    // Stores length of the string
    var len = s.length;

    // Effective shift calculation
    val = val % len;

    // Stores modified string
    var result = "";

    // Right rotation
    if (val > 0)
        result = s.substring(len - val,len)
                 + s.substring(0, len - val);

    // Left rotation
    else
        result
            = s.substring(-val, len )
              + s.substring(0, -val);

    document.write( result);
}

// Driver Code
var s = "abc";
var shift = [
    [ 0, 1 ],
    [ 1, 2 ]
];
stringShift(s, shift);

// This code is contributed by importantly.
</script> 

cab

Time Complexity: O(N)
Auxiliary Space: O(N)

Please refer complete article on Modify a string by performing given shift operations for more details!