- Added solutions by Arne Sommer.

- Added solutions by Packy Anderson.

1 files changed, 75 insertions, 0 deletions

diff --git a/challenge-236/packy-anderson/java/Ch1.java b/challenge-236/packy-anderson/java/Ch1.java
new file mode 100644
index 0000000000..678631bf8d
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+++ b/challenge-236/packy-anderson/java/Ch1.java
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+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.stream.Collectors;
+import java.util.HashMap;
+import java.util.List;
+
+public class Ch1 {
+  public static boolean isExactChangePossible(int[] bills) {
+    // we keep the bills in a "till"
+    HashMap<Integer, Integer> till =
+      new HashMap<Integer, Integer>();
+
+    for (int collected : bills) {
+      // put the bill we collected in the "till"
+      //
+      // using .getOrDefault(collected, 0) yields the value
+      // in the map for the key 'collected' if it exists, or
+      // the specified default (in this case, 0) if it doesn't
+      till.put(
+        collected,
+        till.getOrDefault(collected, 0) + 1
+      );
+
+      // calculate the required change
+      int change_required = collected - 5;
+
+      // loop through the bills we have on hand, making sure
+      // we go from largest to smallest bill
+      List<Integer> keys = new ArrayList<>(till.keySet());
+      Collections.sort(keys, Collections.reverseOrder());
+      for (Integer bill : keys) {
+        // as long as we have more of this bill and
+        // using it would not yield TOO MUCH change
+        while (till.get(bill) > 0 &&
+               change_required - bill >= 0) {
+          // deduct the amount from the required change
+          change_required -= bill;
+
+          // remove the bill from the till
+          till.put(bill, till.get(bill) - 1);
+        }
+      }
+      // if we weren't able to make change, fail
+      if (change_required > 0) {
+          return false;
+      }
+    }
+    return true;
+  }
+
+  public static String joined(int[] ints) {
+    // we're using it more than once, make it a method
+    return Arrays.stream(ints)
+                 .mapToObj(String::valueOf)
+                 .collect(Collectors.joining(", "));
+  }
+
+  public static void solution(int[] bills) {
+    System.out.println("Input: @bills = (" + joined(bills) + ")");
+    boolean output = isExactChangePossible(bills);
+    System.out.println("Output: " + output);
+  }
+
+  public static void main(String[] args) {
+    System.out.println("Example 1:");
+    solution(new int[] {5, 5, 5, 10, 20});
+
+    System.out.println("\nExample 2:");
+    solution(new int[] {5, 5, 10, 10, 20});
+
+    System.out.println("\nExample 3:");
+    solution(new int[] {5, 5, 5, 20});
+  }
+}