From 93927772601b5681953e5e2d5e3ed70d7cc4d667 Mon Sep 17 00:00:00 2001
From: ivan <ivan.li@practiceinsight.io>
Date: Fri, 28 Dec 2018 14:29:42 +0800
Subject: [PATCH] transformed binary search

---
 .../src/main/scala/ch16_bsearch/BSearch.scala | 87 +++++++++++++++++++
 .../test/scala/ch16_bsearch/BSearchTest.scala | 31 +++++++
 2 files changed, 118 insertions(+)
 create mode 100644 scala/src/main/scala/ch16_bsearch/BSearch.scala
 create mode 100644 scala/src/test/scala/ch16_bsearch/BSearchTest.scala

diff --git a/scala/src/main/scala/ch16_bsearch/BSearch.scala b/scala/src/main/scala/ch16_bsearch/BSearch.scala
new file mode 100644
index 0000000..74e2fbe
--- /dev/null
+++ b/scala/src/main/scala/ch16_bsearch/BSearch.scala
@@ -0,0 +1,87 @@
+package ch16_bsearch
+
+object BSearch {
+
+  //find the first index of given value
+  //-1 if not found
+  def findFirstValue(items: Array[Int], target: Int): Int = {
+    require(items.length > 0, "given array is empty")
+    var low = 0
+    var high = items.length - 1
+    while (low <= high) {
+      val mid = low + (high - low) / 2
+      if (items(mid) > target) {
+        high = mid - 1
+      } else if (items(mid) < target) {
+        low = mid + 1
+      } else {
+        //find the value in the array
+        if (mid == 0 || items(mid - 1) != target) {
+          return mid
+        } else {
+          high = mid - 1
+        }
+      }
+    }
+    -1
+  }
+
+  def findLastValue(items: Array[Int], target: Int): Int = {
+    var low = 0
+    var high = items.length - 1
+    while (low <= high) {
+      val mid = low + (high - low) / 2
+      if (items(mid) > target) {
+        high = mid - 1
+      } else if (items(mid) < target) {
+        low = mid + 1
+      } else {
+        //find the target value
+        if (mid == items.length - 1 || items(mid + 1) != target) {
+          return mid
+        } else {
+          low = mid + 1
+        }
+      }
+    }
+    -1
+  }
+
+  def findFirstGreaterThan(items: Array[Int], target: Int): Int = {
+    var low = 0
+    var high = items.length
+    while (low <= high) {
+      val mid = low + (high - low) / 2
+      if (items(mid) >= target) {
+        //find the range
+        if (mid == 0 || items(mid - 1) < target) {
+          return mid
+        } else {
+          high = mid - 1
+        }
+      } else {
+        low = mid + 1
+      }
+    }
+    -1
+  }
+
+  def findLastSmallerThan(items: Array[Int], target: Int): Int = {
+    var low = 0
+    var high = items.length - 1
+    while (low <= high) {
+      var mid = low + (high - low) / 2
+      if (items(mid) <= target) {
+        //find the range
+        if (mid == items.length - 1 || items(mid + 1) > target) {
+          return mid
+        } else {
+          low = mid + 1
+        }
+      } else {
+        high = mid - 1
+      }
+    }
+    -1
+  }
+}
diff --git a/scala/src/test/scala/ch16_bsearch/BSearchTest.scala b/scala/src/test/scala/ch16_bsearch/BSearchTest.scala
new file mode 100644
index 0000000..89da6fa
--- /dev/null
+++ b/scala/src/test/scala/ch16_bsearch/BSearchTest.scala
@@ -0,0 +1,31 @@
+package ch16_bsearch
+
+import org.scalatest.{FlatSpec, Matchers}
+
+class BSearchTest extends FlatSpec with Matchers {
+
+  behavior of "BSearchTest"
+
+  it should "findFirstValue" in {
+    val items = Array(1, 3, 4, 5, 6, 8, 8, 8, 11, 18)
+    BSearch.findFirstValue(items, 8) should equal(5)
+  }
+
+  it should "findLastValue" in {
+    val items = Array(1, 3, 4, 5, 6, 8, 8, 8, 11, 18)
+    BSearch.findLastValue(items, 8) should equal(7)
+  }
+
+  it should "findFirstGreaterThan" in {
+    val items = Array(1, 3, 4, 5, 6, 8, 8, 8, 11, 18)
+    BSearch.findFirstGreaterThan(items, 2) should equal(1)
+    BSearch.findFirstGreaterThan(items, 8) should equal(5)
+  }
+
+  it should "findLastSmallerThan" in {
+    val items = Array(1, 3, 4, 5, 6, 8, 8, 8, 11, 18)
+    BSearch.findLastSmallerThan(items, 2) should equal(0)
+    BSearch.findLastSmallerThan(items, 8) should equal(7)
+  }
+
+}