Reverse Only Letters for coding interview round

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Last Updated: 15 Mar, 2021

Easy

Problem statement

The first line of the input contains ‘T’ denoting the number of test cases.

The first line of each test case contains a string ‘S’.

For every test case, we need to print the reversed string in a new line.

You do not need to print anything, it has already been taken care of. Just implement the given function.

1 <= T <= 10
0 <= |S| <= 5000

Where |S| denotes the length of string 'S'.

Time Limit: 1 Sec

Approaches

01Approach

Approach: Just like in order to reverse a string ‘S’ = “abcd”, we can can swap(S[0], S[3]) and swap(S[1],S[2]) to get new string “dcba”.

Similarly in this problem, we do the same using two pointers while ignoring the non-letter characters.

Eg: S = “a-bcd” we swap(S[0], S[4]) and swap(S[2], S[3]) to get the result.

Algorithm:

In the given string what we can do is maintain two variables one pointer to the 0th position and the other pointing to the ‘N - 1’ position.
If both have letters we swap them and increment the first pointer and decrement second.
Else if the first pointer has a non-letter we just increment it and if the second pointer has a non-letter we decrement it.
We continue it till the first pointer is less than the second pointer.