LeetCode 1417: Reformat The String Solution

Master LeetCode problem 1417 (Reformat The 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.

1417. Reformat The String

Easy

String

Problem Explanation

Explanation

To solve this problem, we need to reformat the string such that no two adjacent characters have the same type (letter or digit). We can achieve this by counting the number of letters and digits in the input string s. If the absolute difference between the counts of letters and digits is not greater than 1, we can proceed to construct the reformatted string by interleaving letters and digits. Otherwise, it is impossible to reformat the string.

Algorithm:

Count the number of letters and digits in the input string s.
Check if the absolute difference between the counts of letters and digits is more than 1. If so, return an empty string.
Initialize two pointers, one for letters and the other for digits, to construct the reformatted string.
Based on which count is higher, start constructing the reformatted string by interleaving letters and digits.
Return the reformatted string.

Time Complexity: O(n), where n is the length of the input string s. Space Complexity: O(n)

Solution Code

class Solution {
    public String reformat(String s) {
        int n = s.length();
        StringBuilder sb = new StringBuilder();
        
        int letterCount = 0, digitCount = 0;
        for (char c : s.toCharArray()) {
            if (Character.isLetter(c))
                letterCount++;
            else
                digitCount++;
        }
        
        if (Math.abs(letterCount - digitCount) > 1)
            return "";
        
        int i = 0, j = 0;
        if (letterCount >= digitCount) {
            i = 0; j = 1;
        } else {
            i = 1; j = 0;
        }
        
        for (char c : s.toCharArray()) {
            if (Character.isLetter(c)) {
                sb.insert(i, c);
                i += 2;
            } else {
                sb.insert(j, c);
                j += 2;
            }
        }
        
        return sb.toString();
    }
}

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