HackerRank-Solutions/General Programming/Basic Programming/Append and Delete/Solution.java

//     Author: Rodney Shaghoulian
//     Github: github.com/RodneyShag
// HackerRank: hackerrank.com/RodneyShag

import java.util.Scanner;

// Case 1: See if we can completely erase String "s" and append String "t". If we need to waste
//         operations to reach "k" operations, we can do so when String "s" has no characters.

// Case 2: See if we can convert String "s" to String "t" without completely erasing String "s". 
//         We keep erasing charcters from String "s" until it becomes a prefix of String "t". We 
//         then add the characters needed to turn String "s" into String "t". If we need to waste 
//         operations to reach "k" operations, we can only do so in groups of 2 by doing an append 
//         and a delete.

public class Solution {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String s = scan.next();
        String t = scan.next();
        int k = scan.nextInt();
        scan.close();
        System.out.println(canConvert(s, t, k) ? "Yes" : "No");
    }    

    private static boolean canConvert(String s, String t, int k) {
        /* Case 1 */
        if (s.length() + t.length() <= k) {
            return true;
        }
        
        /* Case 2 */
        int i = 0; // represents index of 1st non-matching character
        for (   ; i < s.length() && i < t.length(); i++) {
            if (s.charAt(i) != t.charAt(i)) {
                break;
            }
        }
        int minOperations = (s.length() - i) + (t.length() - i);
        return k >= minOperations && (k - minOperations) % 2 == 0;
    }
}