1165. Single-Row Keyboard

Description

There 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.

Constraints

• keyboard.length == 26

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

• 1 <= word.length <= 10^4

• word[i] is an English lowercase letter.

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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

Solutions

Solution 1

/**
 * Time complexity : O(n). Where n is the length of word, since we need to 
 *    traverse the word. An additional constant of O(26) = O(1) is needed 
 *    to iterate through keyboard.
 * Space complexity : O(1). The algorithm requires constant space to store 
 *    indices for 26 letters.
 */

class Solution {
    public int calculateTime(String keyboard, String word) {
        int[] keyIndices = new int[26];
        for(int i = 0; i < keyboard.length(); i++) {
            keyIndices[keyboard.charAt(i)-'a'] = i;
        }
        
        int cost = 0, prev = 0;
        for(char ch: word.toCharArray()) {
            int index = keyIndices[ch-'a'];
            cost += Math.abs(index-prev);
            prev = index;
        }
        return cost;
    }
}

Follow up