Single-Row Keyboard - Practice Coding Problems

Single-Row Keyboard - Problem

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.

Input & Output

Example 1 — Basic Case

$ Input: keyboard = "abcdefghijklmnopqrstuvwxyz", word = "cba"

› Output: 4

💡 Note: Start at 0. Move to 'c' at position 2: |0-2| = 2. Move to 'b' at position 1: |2-1| = 1. Move to 'a' at position 0: |1-0| = 1. Total: 2+1+1 = 4

Example 2 — Custom Layout

$ Input: keyboard = "pqrstuvwxyzabcdefghijklmno", word = "leetcode"

› Output: 73

💡 Note: With custom keyboard layout, characters are at different positions. Calculate distance for each character move.

Example 3 — Single Character

$ Input: keyboard = "abcdefghijklmnopqrstuvwxyz", word = "z"

› Output: 25

💡 Note: Start at position 0, move to 'z' at position 25: |0-25| = 25

Constraints

keyboard.length == 26
keyboard contains each English lowercase letter exactly once
1 ≤ word.length ≤ 10⁴
word[i] is an English lowercase letter

Visualization

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Understanding the Visualization

Input

Keyboard layout and word to type

Process

Calculate finger movement distances

Output

Total time for all movements

Key Takeaway

🎯 Key Insight: Pre-mapping character positions eliminates the need for repeated searches, making the solution efficient.

Asked in

G Google 12 a Amazon 8 M Microsoft 6

The key insight is to map each character to its keyboard position for instant lookup. The optimal approach uses a hash map to precompute character positions, then calculates cumulative distances. Time: O(n), Space: O(1) (since alphabet size is constant).

Common Approaches

Approach	Time	Space	Notes
✓ Brute Force	O(n×m)	O(1)	Search for each character's position in keyboard string for every character in word
Hash Map Optimization	O(n + m)	O(m)	Pre-build a hash map of character positions, then lookup each character in O(1) time

Brute Force — Algorithm Steps

Step 1: Start at position 0
Step 2: For each character in word, search keyboard to find its index
Step 3: Add distance |current_pos - char_pos| to total time
Step 4: Update current position to character position

Visualization

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Step-by-Step Walkthrough

Linear search keyboard for character position

Calculate

Compute distance from current position

Move

Update position and add to total time

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int solution(char* keyboard, char* word) {
    int currentPos = 0;
    int totalTime = 0;
    int wordLen = strlen(word);
    
    for (int i = 0; i < wordLen; i++) {
        char c = word[i];
        // Find position of character in keyboard
        int charPos = 0;
        for (int j = 0; j < 26; j++) {
            if (keyboard[j] == c) {
                charPos = j;
                break;
            }
        }
        // Add time to move from current position to character position
        int distance = currentPos - charPos;
        if (distance < 0) distance = -distance;
        totalTime += distance;
        // Update current position
        currentPos = charPos;
    }
    
    return totalTime;
}

int main() {
    char keyboard[100];
    char word[100];
    
    fgets(keyboard, sizeof(keyboard), stdin);
    keyboard[strcspn(keyboard, "\n")] = 0;
    
    fgets(word, sizeof(word), stdin);
    word[strcspn(word, "\n")] = 0;
    
    int result = solution(keyboard, word);
    printf("%d\n", result);
    
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n×m)

For each of n characters in word, search through m=26 characters in keyboard

✓ Linear Growth

Space Complexity

O(1)

Only using variables to track position and total time

✓ Linear Space

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Brute Force — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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