TheAlgorithms · siriak · Oct 27, 2021 · Oct 2, 2021 · Oct 2, 2021 · Oct 24, 2021
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+package Searches;
+
+import static java.lang.String.format;
+
+import java.util.Random;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.stream.IntStream;
+
+/**
+ * The UpperBound method is used to return an index pointing to the first element in the range
+ * [first, last) which has a value greater than val, or the last index if no such element exists
+ * i.e. the index of the next smallest number just greater than that number. If there are multiple
+ * values that are equal to val it returns the index of the first such value.
+ *
+ * <p>This is an extension of BinarySearch.
+ *
+ * <p>Worst-case performance O(log n) Best-case performance O(1) Average performance O(log n)
+ * Worst-case space complexity O(1)
+ *
+ * @author Pratik Padalia (https://github.com/15pratik)
+ * @see SearchAlgorithm
+ * @see BinarySearch
+ */
+class UpperBound implements SearchAlgorithm {
+
+  // Driver Program
+  public static void main(String[] args) {
+    // Just generate data
+    Random r = ThreadLocalRandom.current();
+
+    int size = 100;
+    int maxElement = 100000;
+
+    Integer[] integers =
+        IntStream.generate(() -> r.nextInt(maxElement))
+            .limit(size)
+            .sorted()
+            .boxed()
+            .toArray(Integer[]::new);
+
+    // The element for which the upper bound is to be found
+    int val = integers[r.nextInt(size - 1)] + 1;
+
+    UpperBound search = new UpperBound();
+    int atIndex = search.find(integers, val);
+
+    System.out.println(
+        format(
+            "Val: %d. Upper Bound Found %d at index %d. An array length %d",
+            val, integers[atIndex], atIndex, size));
+
+    boolean toCheck = integers[atIndex] > val || integers[size - 1] < val;
+    System.out.println(
+        format(
+            "Upper Bound found at an index: %d. Is greater or max element: %b", atIndex, toCheck));
+  }
+
+  /**
+   * @param array is an array where the UpperBound value is to be found
+   * @param key   is an element for which the UpperBound is to be found
+   * @param <T>   is any comparable type
+   * @return index of the UpperBound element
+   */
+  @Override
+  public <T extends Comparable<T>> int find(T[] array, T key) {
+    return search(array, key, 0, array.length - 1);
+  }
+
+  /**
+   * This method implements the Generic Binary Search
+   *
+   * @param array The array to make the binary search
+   * @param key   The number you are looking for
+   * @param left  The lower bound
+   * @param right The upper bound
+   * @return the location of the key
+   */
+  private <T extends Comparable<T>> int search(T[] array, T key, int left, int right) {
+    if (right <= left) {
+      return left;
+    }
+
+    // find median
+    int median = (left + right) >>> 1;
+    int comp = key.compareTo(array[median]);
+
+    if (comp < 0) {
+      // key is smaller, median position can be a possible solution
+      return search(array, key, left, median);
+    } else {
+      // key we are looking is greater, so we must look on the right of median position
+      return search(array, key, median + 1, right);
+    }
+  }
+}