The Long Pressed Name interview question presents you with two strings: a name and a typed string. When someone types a name on a keyboard, they might accidentally long-press a key, causing a character to be repeated one or more times. Your objective is to write an algorithm that checks if the typed string could be a valid result of typing the name string, considering these potential long-pressed characters.
This string coding problem is a classic gauge of a candidate's ability to carefully traverse arrays or strings without going out of bounds. It's heavily favored for entry-level and mid-level roles because it mimics a realistic user-input validation scenario. It specifically tests your edge-case management—such as when the typed string has extra characters at the end, or when it misses a character entirely.
The definitive approach here is the Two Pointers pattern. You maintain one pointer i for the original name string and another pointer j for the typed string. As you iterate, you compare the characters. If they match, you advance both pointers. If they don't match, you check if the current character in typed is a valid long-press (i.e., it matches the previous character in typed and name). If neither condition is met, the string is invalid.
Let name = "alex" and typed = "aaleex".
i=0 ('a'), j=0 ('a'): Match. Advance both. i=1, j=1.i=1 ('l'), j=1 ('a'): Mismatch. But typed[1] ('a') matches typed[0], so this is a long press. Advance j only. i=1, j=2.i=1 ('l'), j=2 ('l'): Match. Advance both. i=2, j=3.i=2 ('e'), j=3 ('e'): Match. Advance both. i=3, j=4.i=3 ('x'), j=4 ('e'): Mismatch. typed[4] matches typed[3]. Advance j. i=3, j=5.i=3 ('x'), j=5 ('x'): Match. Advance both. i=4, j=6.
Pointer i has reached the end of name, meaning all essential characters were matched.A frequent mistake is not handling the end of the strings correctly. For example, if name = "alex" and typed = "alexxxy", candidates might reach the end of name but forget to verify that the remaining characters in typed are all valid long-presses of the final character 'x'. The stray 'y' should cause the function to return false. Another common error is accessing typed[j-1] when j=0, leading to index out-of-bounds exceptions.
To excel at the Long Pressed Name interview pattern, rigorously practice your while-loop conditions. Whenever you use Two Pointers of uneven pacing, map out three explicit cases: 1) What happens when characters match? 2) What happens when they don't match but it's a valid duplicate? 3) What happens if it's an invalid character? Drawing out these state transitions before writing code prevents messy logic.