String generation

Problem Statement

String generation Problem Description Given a string S1 of length L1 consisting of Latin uppercase alphabets only and a string S2 of length L2 consisting of characters 'T' and 'F' only. Generate a lexicographically smallest string S of length (L1 + L2 - 1) such that a substring of length L1 in string S starting at index i (0 <= i < L2) is equal to S1 if and only if i-th element of S2 is 'T' (without quotes) else not. If no such string can be generated, print "-1" (without quotes). Notes A string a is lexicographically smaller than a string b if and only if one of the following holds: a is a prefix of b, but a != b; in the first position where a and b differ, the string a has a letter that appears earlier in the alphabet than the corresponding letter in b. Find the lexicographically smallest string S which satisfies the given condition. Function Description Complete the solve function. This function takes the following 2 parameters and returns the answer. S1: Represents a string S