Program to find second largest digit in a string using Python

When working with alphanumeric strings, we often need to extract and analyze the numerical digits. This program finds the second largest digit in a string, returning -1 if there aren't enough unique digits.

So, if the input is like s = "p84t3ho1n", then the output will be 4 as the digits are [1,3,4,8], so second largest digit is 4.

Algorithm

To solve this, we will follow these steps −

• Create a set to store unique digits

• For each character in the string, do

  • If character is a digit, add it to the set as integer

• If size of set <= 1, then

  • Return -1 (not enough unique digits)

• Sort the digits and return the second largest

Example

def solve(s):
    digit_set = set()
    for char in s:
        if char.isdigit():
            digit_set.add(int(char))
    
    if len(digit_set) <= 1:
        return -1
    
    sorted_digits = sorted(list(digit_set))
    return sorted_digits[-2]  # Second largest

# Test with example
s = "p84t3ho1n"
result = solve(s)
print(f"Input: {s}")
print(f"Second largest digit: {result}")

Input: p84t3ho1n
Second largest digit: 4

Testing Edge Cases

Let's test with different scenarios ?

def solve(s):
    digit_set = set()
    for char in s:
        if char.isdigit():
            digit_set.add(int(char))
    
    if len(digit_set) <= 1:
        return -1
    
    sorted_digits = sorted(list(digit_set))
    return sorted_digits[-2]

# Test cases
test_cases = ["p84t3ho1n", "hello", "a1b2c", "987654321", "aaa1aaa"]

for test in test_cases:
    result = solve(test)
    print(f"'{test}' ? {result}")

'p84t3ho1n' ? 4
'hello' ? -1
'a1b2c' ? 1
'987654321' ? 8
'aaa1aaa' ? -1

How It Works

The solution uses a set to automatically handle duplicate digits. We iterate through each character, check if it's a digit using isdigit(), and add it to our set as an integer. Finally, we sort the unique digits and return the second largest element using index [-2].

Conclusion

This program efficiently finds the second largest digit by using a set to eliminate duplicates and sorting to find the required element. It handles edge cases by returning -1 when there aren't enough unique digits.