1663. Smallest String With A Given Numeric Value

Problem

Tags: String, Greedy

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.

Example 1:

Input: n = 3, k = 27
Output: "aay"
Explanation: The numeric value of the string is 1 + 1 + 25 = 27, and it is the smallest string with such a value and length equal to 3.

Example 2:

Input: n = 5, k = 73
Output: "aaszz"

Constraints:

• 1 <= n <= 10^5
• n <= k <= 26 * n

Code

C

// 1663. Smallest String With A Given Numeric Value (12/16/54191)
// Runtime: 37 ms (50.56%) Memory: 15.26 MB (75.66%) 

char* getSmallestString (int n, int k) {
    char* ans = (char*)calloc(n + 1, sizeof(char));

    for (int i = n - 1; i >= 0; i--) {
        int left = k - i;
        ans[i] = left >= 27 ? 'z' : 'a' + left - 1;
        k -= ans[i] - 'a' + 1;
    }

    return ans;
}

TS

// 1663. Smallest String With A Given Numeric Value (1/6/54192)
// Runtime: 153 ms (85.32%) Memory: 48.50 MB (86.24%) 

function getSmallestString(n: number, k: number): string {
    k -= n;
    const tail = "z".repeat(Math.floor(k / 25));
    const body = k % 25 === 0 ? "" : String.fromCharCode(k % 25 + 97);
    return (body + tail).padStart(n, "a");
};