LeetCode 1545: Find Kth Bit in Nth Binary String Solution

Master LeetCode problem 1545 (Find Kth Bit in Nth Binary String), 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.

1545. Find Kth Bit in Nth Binary String

Medium

String Recursion Simulation

Problem Explanation

Explanation:

To solve this problem, we can observe that the binary strings follow a recursive pattern based on the previous string. We can simulate the generation of each string up to the nth string and then find the kth bit in the final string.

Start with the base case: S1 = "0".
For i > 1, generate Si based on Si-1 using the given formula.
Repeat this process for n iterations to generate Sn.
Finally, return the kth bit in Sn.

Time complexity: O(2^n)
Space complexity: O(2^n) :

Solution Code

class Solution {
    public char findKthBit(int n, int k) {
        return generateString(n).charAt(k - 1);
    }
    
    private String generateString(int n) {
        if (n == 1) {
            return "0";
        }
        
        String prev = generateString(n - 1);
        return prev + "1" + invertAndReverse(prev);
    }
    
    private String invertAndReverse(String s) {
        StringBuilder sb = new StringBuilder();
        for (char c : s.toCharArray()) {
            sb.append(c == '0' ? '1' : '0');
        }
        return sb.reverse().toString();
    }
}

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