Print the largest integer formed by inserting digit X in given string

Given a string S of size N representing a large integer value, and a positive digit X, the task is to print the largest integer formed by inserting the digit X in the string S.

Examples:

Input: S = “99”, X = 9
Output: 999
Explanation: 
The largest number that can be formed is 999 after inserting 9 into “99”.

Input: S = “-13”, X = 2
Output: -123
Explanation: 
The largest number that can be formed is -123 after inserting 2 into “-13”.

Approach: The problem can be solved by iterating over the character of the string S. Follow the steps below to solve this problem:

• If the number S is positive, then perform the following steps:
  • Iterate in the range [0,  N-1] using the variable i and perform the following steps:
    • If S[i] is less than X then insert the digit X before S[i] and break the loop.
  • If none of the above cases satisfy, then append the digit X at the end of the string S.
• Else, if the number S is negative, then perform the following steps:
  • Iterate in the range [0, N-1] in using the variable i and perform the following steps:
    • If S[i] is less than X, then insert the digit X before S[i] and break the loop.
  • If none of the above cases satisfy, then append the digit X at the end of the string S.
• Finally, print the largest possible string, represented by S.

Below is the implementation of the above approach:

Python3

# Python program for the above approach

# Function to find Largest Number after
# insertion of a digit
def largestValue(S, X):

    # If S is negative
    if S[0] == '-':
        f = 0
        # Iterate through characters of S
        for i, val in enumerate(S):
            if i == 0:
                continue

            # If digit x is less
            # than S[i] insert digit
            # after X
            if X < int(val):
                f = 1
                S = S[:i] + str(X) + S[i:]
                break

        if f == 0:
            S = S + str(X)

    # If S is positive
    else:
        f = 0

        # If x > S[i] insert x
        for i, val in enumerate(S):
            if X > int(val):
                f = 1
                S = S[:i] + str(X) + S[i:]
                break

        if f == 0:
            S = S + str(X)

    # Return the answer
    return S


# Driver Code

# Given Input
S = "-13"
X = 2

# Function Call
print(largestValue(S, X))

Output

-123

Time Complexity: O(N)
Auxiliary Space: O(1)