SDE - 1

Key idea - 2 pointer method
Approach - place one pointer p1 on start, 2nd pointer p2 on end. Move p1 to right and p2 to left unless we find a non special character for both, if found for both, swap the values pointed by p1 and p2.
Steps:
S1: Pointer p1 at start and p2 at end index
S2: While p1! = p2 and arr[p1] is special character, move p1 to right
S3: While p1! = p2 and arr[p2] is special character, move p2 to left
S4: Swap values pointed by index p1 and p2.
S5: Follow above steps until p1 < p2.

Approach - Using Binary Search - In this approach, we will first find the string with the minimum length among all the strings in the array and store it as prefix because the shortest string is the longest possible common prefix. We will also define a function isCommon(ARR, prefix, length, N) to whether the string prefix is a common prefix for all the strings in the array ARR or not. We will start the search by setting start as 0 and end as the length of prefix. At each iteration, we will set mid as (start+end)/2. Each time search space is divided into two equal parts, one of them is discarded because it is sure that it doesn't contain the solution.