Single-row keyboard

Time: O(N); Space: O(1); easy

here is a special keyboard with all keys in a single row.

Given a string keyboard of length 26 indicating the layout of the keyboard (indexed from 0 to 25), initially your finger is at index 0.

To type a character, you have to move your finger to the index of the desired character.

The time taken to move your finger from index i to index j is |i - j|.

You want to type a string word. Write a function to calculate how much time it takes to type it with one finger.

Example 1:

Input: keyboard = “abcdefghijklmnopqrstuvwxyz”, word = “cba”

Output: 4

Explanation:

  • The index moves from 0 to 2 to write ‘c’ then to 1 to write ‘b’ then to 0 again to write ‘a’.

  • Total time = 2 + 1 + 1 = 4.

Example 2:

Input: keyboard = “pqrstuvwxyzabcdefghijklmno”, word = “leetcode”

Output: 73

Constraints:

  • len(keyboard) == 26

  • keyboard contains each English lowercase letter exactly once in some order.

  • 1 <= word.length <= 10^4

  • word[i] is an English lowercase letter.

[1]:

class Solution1(object):
    """
    Time: O(N)
    Space: O(1)
    """
    def calculateTime(self, keyboard, word):
        """
        :type keyboard: str
        :type word: str
        :rtype: int
        """
        lookup = {c:i for i, c in enumerate(keyboard)}

        result, prev = 0, 0
        for c in word:
            result += abs(lookup[c]-prev)
            prev = lookup[c]

        return result

[2]:

s = Solution1()

keyboard = "abcdefghijklmnopqrstuvwxyz"
word = "cba"
assert s.calculateTime(keyboard, word) == 4

keyboard = "pqrstuvwxyzabcdefghijklmno"
word = "leetcode"
assert s.calculateTime(keyboard, word) == 73