Find the lexicographically minimal string, whose sum is equal to K

Each letter, a-z, is assigned values in the following way: a: 1, b: 2, …, z: 26. You are given string, S, consisting of lowercase English letters and an integer, K. Find the lexicographically minimal string, whose sum is equal to K.

Find the lexicographically minimal string whose sum is K, then why are we provided with S. Please provide the link to the problem if possible…

Please see the Q2 here: https://codingblocks.com/resources/iq-arcesium-nishant/

It was asked in Arcesium

According to me you need to find minimum substring with sum=K. So if you save each character in a 1D array, and then take cummalative sum while iterating over the array. Then for each index i, find an index for ai + K in that array. This will work in O(N) i guess