Please help in building solution

How to solve below problem statement.

given a string s which contains only curly braces and questions was what is the minimum number of operations to become it valid expression and return corrected string. There are three operations:

insert { or } in any position

delete { or } in any position. flip any position so { change by } or vice versa.

Please provide full explaination. Thanks in advance. link

Please help in thought process .Link of Problem

You can check many solutions have passed main test also which was only 67 and now it has 100 test cases , don't you think solutions should be rejudged.

Question's Pic

testcases

Hi can any one please explain the approach to solve this question; (https://www.codechef.com/START24B/problems/PALINLOVE) Thanks in advance.

Please explain how to solve this problem. https://cses.fi/problemset/task/1110

There is an array of strings. Suppose there is a string whose last character matches with the first character of another string. In that case those two form a ring. You have the find the maximum length of the ring formed by the strings in the array. Let me explain the problem with an example. Suppose the array of strings is {ear, track, tired, rat, doe}. Here the maximum ring will be ear->rat->tired->doe>ear. So, the length will be 4.

If possible please provide code also .