Check if Word Equals Summation of Two Words - Video Solutions

Problem Overview: Each lowercase character from 'a' to 'j' represents a digit from 0 to 9. Converting a word means replacing every character with its corresponding digit and interpreting the resulting string as a number. The task is to check whether the numeric value of firstWord plus secondWord equals the numeric value of targetWord.

Approach 1: Brute Force Conversion and Comparison (O(n) time, O(n) space)

The direct approach converts each word into its numeric representation using a mapping from characters to digits. Iterate through every character, compute digit = c - 'a', append that digit to a string (or buffer), and then convert the resulting string into an integer using a standard parsing function. After computing values for firstWord, secondWord, and targetWord, compare whether the first two sum to the third. This method is straightforward and mirrors the problem statement exactly. The extra space comes from building intermediate digit strings before parsing. Time complexity is O(n), where n is the total length of all words.

Approach 2: Mapping and Direct Calculation (O(n) time, O(1) space)

You can avoid intermediate strings by constructing the numeric value directly during traversal. Start with value = 0, then iterate through each character and update value = value * 10 + (c - 'a'). This simulates digit concatenation mathematically. Apply the same logic to all three words and check whether value(firstWord) + value(secondWord) == value(targetWord). This eliminates parsing overhead and reduces memory usage since only integers are stored. The time complexity remains O(n) because each character is processed once, but the space complexity drops to O(1).

This problem mainly tests basic manipulation of string characters and simple digit construction, which is common in simulation problems. The numeric construction step also mirrors patterns seen in math-based string conversions where characters represent digits.

Recommended for interviews: The mapping and direct calculation approach. It demonstrates that you understand how digit concatenation works without relying on string parsing utilities. The brute force version shows correct interpretation of the problem, but the constant-space calculation is cleaner and typically what interviewers expect for simple conversion tasks.