1663. Smallest String With A Given Numeric Value.md

1663. Smallest String With A Given Numeric Value

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the second one in Weekly Contest 216.

leetcode Daily Challenge on January 28th, 2021.

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Difficulty : Medium

Related Topics : Greedy

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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

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Solution

• mine
  • Java
    • Runtime: 26 ms, faster than 70.54%, Memory Usage: 39.3 MB, less than 70.22% of Java online submissions

      // O(N)time
      // O(N)space
      public String getSmallestString(int n, int k) {
          int count = k / 26;
          int mod = k % 26;
      
          StringBuilder res = new StringBuilder();
          int head = n - count;
          while(head > 1 || mod == 0){
              if(mod == 0){
                  count--;
                  mod = 26;
                  head++;
              }
              res.append('a');
              mod--;
              head--;
          }
          res.append((char)('a' + mod - 1));
          while(count > 0){
              res.append('z');
              count--;
          }
          return res.toString();
      }
      

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• the most votes

• Runtime: 11 ms, faster than 90.05%, Memory Usage: 38.9 MB, less than 81.04% of Java online submissions

  // O(N)time
  // O(N)space
  public String getSmallestString(int n, int k) {
      char[] ca = new char[n];
      Arrays.fill(ca, 'a');
      k -= n; // Guarantee each character value is at least 1.
      for (int i = n - 1; i >= 0 && k > 0; --i) {
          ca[i] += Math.min(25, k);
          k -= Math.min(k, 25);
      }
      return String.valueOf(ca);
  }
  

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