LeetCode 2496 - Maximum Value of a String in an Array

This problem asks us to compute the maximum value of strings in an array according to a specific definition of value. Each string can either be entirely numeric or alphanumeric. If a string consists only of digits, its value is the integer it represents.

leetcodeeasyarraystring

LeetCode Problem 2496

Difficulty: 🟢 Easy
Topics: Array, String

Solution

Problem Understanding

This problem asks us to compute the maximum value of strings in an array according to a specific definition of value. Each string can either be entirely numeric or alphanumeric. If a string consists only of digits, its value is the integer it represents. If it contains any letters, its value is the length of the string. We are given an array of strings, strs, and need to return the largest value among all strings in the array.

The input strs is a list of strings where each string consists of lowercase letters and digits only. The constraints tell us that the number of strings is moderate (1 <= strs.length <= 100) and that string lengths are small (1 <= strs[i].length <= 9). This means a straightforward linear scan is feasible. Edge cases include strings with leading zeros, strings that are completely numeric but represent zero, and strings that mix letters and digits.

The expected output is a single integer representing the maximum value according to the rules defined.

Approaches

The brute-force approach is simple: iterate through each string, check if it consists only of digits or contains letters, compute its value according to the rules, and track the maximum. This is correct and efficient enough given the small input constraints, but the main insight is that we can combine the checks and computation in a single pass, without additional data structures or preprocessing.

The key observation is that we only need two operations per string: determine if it is numeric and then either compute the integer value or the string length. Since the maximum possible integer is small (9-digit number at most), integer conversion is safe and efficient. This allows a straightforward linear scan to solve the problem optimally.

Approach Time Complexity Space Complexity Notes
Brute Force O(n * m) O(1) Iterate through strings, check numeric, compute value
Optimal O(n * m) O(1) Single-pass scan, compute value inline, track max

n is the number of strings, m is the maximum string length.

Algorithm Walkthrough

  1. Initialize a variable max_value to zero. This will track the maximum value found so far.
  2. Iterate over each string s in strs.
  3. For each string, check if it contains only digits. In Python, we can use s.isdigit(). In Go, we iterate through each character and ensure all are digits.
  4. If the string is numeric, convert it to an integer using int(s) in Python or strconv.Atoi(s) in Go, and assign it to a variable val.
  5. If the string contains any letters, set val to the length of the string len(s).
  6. Compare val with max_value and update max_value if val is greater.
  7. After iterating through all strings, return max_value.

Why it works: The algorithm examines each string exactly once, computes its value according to the problem definition, and keeps track of the largest value. Because each string is processed independently and the comparison is correct, the returned value is guaranteed to be the maximum.

Python Solution

from typing import List

class Solution:
    def maximumValue(self, strs: List[str]) -> int:
        max_value = 0
        for s in strs:
            if s.isdigit():
                val = int(s)
            else:
                val = len(s)
            if val > max_value:
                max_value = val
        return max_value

In this implementation, we initialize max_value to zero. For each string, we use isdigit() to determine if the string is numeric. If numeric, we convert it to an integer. Otherwise, we use the string length. We update max_value whenever we encounter a larger value. This follows the algorithm exactly.

Go Solution

import (
    "strconv"
    "unicode"
)

func maximumValue(strs []string) int {
    maxValue := 0
    for _, s := range strs {
        numeric := true
        for _, ch := range s {
            if !unicode.IsDigit(ch) {
                numeric = false
                break
            }
        }
        var val int
        if numeric {
            v, _ := strconv.Atoi(s)
            val = v
        } else {
            val = len(s)
        }
        if val > maxValue {
            maxValue = val
        }
    }
    return maxValue
}

In Go, we manually check each rune in the string to see if it is a digit using unicode.IsDigit. If the string is numeric, we convert it with strconv.Atoi. Otherwise, we take its length. We track maxValue in the same way as Python.

Worked Examples

Example 1: ["alic3","bob","3","4","00000"]

String Numeric? Value max_value
"alic3" No 5 5
"bob" No 3 5
"3" Yes 3 5
"4" Yes 4 5
"00000" Yes 0 5

Output: 5

Example 2: ["1","01","001","0001"]

String Numeric? Value max_value
"1" Yes 1 1
"01" Yes 1 1
"001" Yes 1 1
"0001" Yes 1 1

Output: 1

Complexity Analysis

Measure Complexity Explanation
Time O(n * m) Each string of length m is checked and potentially converted; n strings in total.
Space O(1) Only a single variable is used to track the maximum; no extra data structures.

The algorithm is linear in the number of strings and string lengths, which is efficient given the constraints.

Test Cases

# Provided examples
assert Solution().maximumValue(["alic3","bob","3","4","00000"]) == 5  # mixed letters and digits
assert Solution().maximumValue(["1","01","001","0001"]) == 1          # leading zeros

# Additional edge cases
assert Solution().maximumValue(["a"]) == 1                             # single letter
assert Solution().maximumValue(["0"]) == 0                             # single zero
assert Solution().maximumValue(["000"]) == 0                           # multiple zeros
assert Solution().maximumValue(["abc","defgh","12"]) == 5             # mix of string lengths and numeric
assert Solution().maximumValue(["123456789","abcdefgh"]) == 9         # largest numeric vs largest length
assert Solution().maximumValue([""]) == 0                              # empty string edge case, if allowed
Test Why
["alic3","bob","3","4","00000"] Checks mixed numeric and alphanumeric strings
["1","01","001","0001"] Checks numeric strings with leading zeros
["a"] Single-letter string
["0"] Single zero numeric string
["000"] Multiple zeros numeric string
["abc","defgh","12"] Combination of string lengths and numeric
["123456789","abcdefgh"] Max numeric vs max length
[""] Edge case of empty string, if allowed

Edge Cases

One important edge case is strings with leading zeros, like "001". Converting this to an integer should yield 1, which is handled correctly with standard integer conversion. Another edge case is strings that are entirely zeros, like "00000", which evaluates to zero numerically even though its length is greater than zero. Strings with both letters and digits, such as "a1b2", should always evaluate to their length, which is correctly handled by the isdigit() check. Finally, an empty string, if present, should be treated as length zero, and our implementation naturally returns zero without error.