implement the findProof method. The method should

1) Add one extra coin to the miner's account in the ledger 2) Convert the new ledger to a String (ledgeStr) 3) Search for a "proof" where the result of hash(ledgerStr + proof) has NUM_ZEROES leading zeroes,

import static java.lang.System.out; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.HashMap; import java.util.Map; public class Miner { public static int NUM_ZEROES = 22; private String name; public Miner(String name) { this.name = name; } public String findProof(Map ledger) throws Exception { return null; } public static String hash(String s) throws NoSuchAlgorithmException { MessageDigest md = MessageDigest.getInstance("SHA-256"); md.update(s.getBytes()); byte[] data = md.digest(); StringBuffer sb = new StringBuffer(); for (int i=0; i ledger = new HashMap(); ledger.put("Alice", 42); ledger.put("Bob", 316); ledger.put("Charlie", 19); Miner alice = new Miner("Alice"); out.println(alice.findProof(ledger)); } }