diff --git a/CrossTrainingIII.java b/CrossTrainingIII.java
new file mode 100644
index 0000000..41867e5
--- /dev/null
+++ b/CrossTrainingIII.java
@@ -0,0 +1,63 @@
+import java.util.*;
+
+public class CrossTrainingIII {
+    /**
+     * Common Numbers Of Two Arrays I(Array version)
+     * <p>
+     * Find all numbers that appear in both of the two unsorted arrays, return the
+     * common numbers in increasing order.
+     */
+    public List<Integer> common(int[] a, int[] b) {
+        Arrays.sort(a);
+        Arrays.sort(b);
+        List<Integer> result = new ArrayList<>();
+
+        int i = 0;
+        int j = 0;
+
+        while (i < a.length && j < b.length) {
+            if (a[i] == b[j]) {
+                result.add(a[i]);
+                i++;
+                j++;
+            } else if (a[i] > b[j]) {
+                j++;
+            } else {
+                i++;
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Largest Rectangle In Histogram
+     * <p>
+     * Given a non-negative integer array representing the heights of a list of
+     * adjacent bars. Suppose each bar has a width of 1. Find the largest
+     * rectangular area that can be formed in the histogram.
+     */
+    public int largest(int[] array) {
+        int result = 0;
+        Deque<Integer> stack = new ArrayDeque<>();
+        for (int i = 0; i < array.length; i++) {
+            if (stack.isEmpty()) {
+                stack.offerLast(i);
+            } else if (array[stack.peekLast()] > array[i]) {
+                int prev = 0;
+                int prevMax = 0;
+                while (!stack.isEmpty() && array[stack.peekLast()] > array[i]) {
+                    prev = stack.pollLast();
+                    prevMax = array[prev];
+                }
+                prev = stack.isEmpty() ? -1 : prev;
+
+                result = Math.max((i - 1 - prev) * prevMax, result);
+            } else {
+                stack.offerLast(i);
+            }
+        }
+        result = Math.max((array.length - stack.peekFirst()) * array[stack.peekFirst()], result);
+
+        return result;
+    }
+}
diff --git a/DFSII.java b/DFSII.java
index 4097979..9efd46c 100644
--- a/DFSII.java
+++ b/DFSII.java
@@ -351,6 +351,9 @@ public int[] keepDistance(int k) {
     }
 
     private boolean keepDistance(int[] result, int n) {
+        if (n == 0) {
+            return true;
+        }
         for (int i = 0; i + n + 1 < result.length; i++) {
             if (result[i] == 0 && result[i + n + 1] == 0) {
                 result[i] = n;