1663. Smallest String With A Given Numeric Value

The numeric value of a lowercase character is defined as its position (1-indexed) in the alphabet, so the numeric value of a is 1, the numeric value of b is 2, the numeric value of c is 3, and so on.

The numeric value of a string consisting of lowercase characters is defined as the sum of its characters’ numeric values. For example, the numeric value of the string “abe” is equal to 1 + 2 + 5 = 8.

You are given two integers n and k. Return the lexicographically smallest string with length equal to n and numeric value equal to k.

Note that a string x is lexicographically smaller than string y if x comes before y in dictionary order, that is, either x is a prefix of y, or if i is the first position such that x[i] != y[i], then x[i] comes before y[i] in alphabetic order.

class Solution {
public:
    string getSmallestString(int n, int k) {
        string res = "";
        while(k) {
            if(n == k)
                res += 'a';
            else {
                
                int alpha = min(k-n+1,26);
                res += ('a' + alpha-1);
            }
            n--; 
            k -= (res.back() - 'a' + 1);
        }
        
        reverse(res.begin(), res.end());
        return res;
    }
};