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  1. Prepare
  2. Algorithms
  3. Implementation
  4. Sequence Equation
  5. Discussions

Sequence Equation

  • RodneyShag
     + 41 comments

    Simple solution with explanation

    From my HackerRank solutions.

    Our input provides us n values of x and p(x)

    p(x) is a one-to-one function, so it has an inverse. We create the function representing the inverse of p(x), and represent it as an array: int [] p_inverse

    We need to find a y where p(p(y)) = x. This equation can be rewritten as
    y = p_inverse(p_inverse(x)), which is the version of the equation we use to calculate and print y.

    import java.util.Scanner;

public class Solution {
    public static void main(String [] args) {
        /* Create function: p_inverse */
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int [] p_inverse = new int[n + 1];
        for (int x = 1; x <= n; x++) {
            int px = scan.nextInt();
            p_inverse[px] = x;
        }
        scan.close();
        
        /* Calculate and print each y */
        for (int x = 1; x <= n; x++) {
            int y = p_inverse[p_inverse[x]];
            System.out.println(y);
        }
    }
}

    Let me know if you have any questions.