LeetCode 3438: Find Valid Pair of Adjacent Digits in String Solution

Master LeetCode problem 3438 (Find Valid Pair of Adjacent Digits in String), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

3438. Find Valid Pair of Adjacent Digits in String

Easy

Hash Table String Counting

Problem Explanation

Explanation:

To solve this problem, we will iterate over the string s from left to right, keeping track of the frequency of each digit. We will check adjacent pairs of digits to see if they form a valid pair according to the given conditions. If we find a valid pair, we return it; otherwise, we continue iterating until the end of the string.

Algorithm:

Initialize a frequency map to keep track of the count of each digit in the string.
Iterate over the string from left to right.
For each pair of adjacent digits, check if they form a valid pair.
If a valid pair is found, return the pair.
If no valid pair is found after iterating through the entire string, return an empty string.

Time Complexity: O(n), where n is the length of the input string s. Space Complexity: O(1) - Although we use a map to store the frequency of digits, the space used is constant since there are only 9 possible digits.

Solution Code

class Solution {
    public String findValidPair(String s) {
        Map<Character, Integer> freq = new HashMap<>();
        
        for (int i = 0; i < s.length() - 1; i++) {
            char curr = s.charAt(i);
            char next = s.charAt(i + 1);
            
            freq.put(curr, freq.getOrDefault(curr, 0) + 1);
            freq.put(next, freq.getOrDefault(next, 0) + 1);
            
            if (curr != next && freq.get(curr) == (curr - '0') && freq.get(next) == (next - '0')) {
                return "" + curr + next;
            }
        }
        
        return "";
    }
}

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