LeetCode 880: Decoded String at Index Solution

Master LeetCode problem 880 (Decoded String at Index), a medium 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.

880. Decoded String at Index

Medium

String Stack

Problem Explanation

Explanation:

To solve this problem, we need to simulate the decoding process and keep track of the length of the decoded string in order to determine the kth letter. We can iterate through the encoded string character by character, updating the length of the decoded string according to the rules provided. When the length of the decoded string exceeds k, we can backtrack to find the exact kth letter.

Iterate through the encoded string character by character.
If the character is a digit, update the length of the decoded string by multiplying it with the digit value.
If the character is a letter, increment the length of the decoded string by 1.
Keep track of the kth letter by decrementing k whenever the length of the decoded string becomes larger than k.
When the length of the decoded string equals or surpasses k, backtrack through the encoded string to find the kth letter.

Time Complexity: O(n), where n is the length of the encoded string. Space Complexity: O(1)

Solution Code

class Solution {
    public String decodeAtIndex(String s, int k) {
        long size = 0;
        for (char c : s.toCharArray()) {
            if (Character.isDigit(c)) {
                size *= (c - '0');
            } else {
                size++;
            }
        }
        
        for (int i = s.length() - 1; i >= 0; i--) {
            char c = s.charAt(i);
            k %= size;
            if (k == 0 && Character.isLetter(c)) {
                return Character.toString(c);
            }
            
            if (Character.isDigit(c)) {
                size /= (c - '0');
            } else {
                size--;
            }
        }
        
        throw new IllegalArgumentException("Invalid input");
    }
}

Try It Yourself

Loading code editor...

Frequently Asked Questions

How to solve LeetCode 880 (Decoded String at Index)?

This page provides optimized solutions for LeetCode problem 880 (Decoded String at Index) in Java, C++, and Python, along with a detailed explanation and an interactive code editor to test your code.

What is the time complexity of LeetCode 880 (Decoded String at Index)?

The time complexity for LeetCode 880 (Decoded String at Index) varies by solution. Check the detailed explanation section for specific complexities in Java, C++, and Python implementations.

Can I run code for LeetCode 880 on DevExCode?

Yes, DevExCode provides an interactive code editor where you can write, test, and run your code for LeetCode 880 in Java, C++, or Python.

Back to LeetCode Solutions