02 (1) find first "..." in sorted array using binary search

stevencooks · stevencooks · commit 993b820ab9da · 2015-08-23T23:41:44.000-04:00
diff --git a/binarysearch/_02_FirstBadVersion/README.md b/binarysearch/_02_FirstBadVersion/README.md
@@ -0,0 +1,23 @@
+### Find Bad Version (find first "..." element in sorted array)
+
+To make life easier, we can consider the very easy situation, only one number exists.
+
+```java
+/**
+ ********************************************************************
+ * case I  : left & right             right    left
+                  |                     |        |
+          index   0          ===>      -1        0                
+          isBad  true                 (null)    true
+    expect = 1 => return left + 1  (return the order not the index of bad version)        
+ ********************************************************************
+ * case II : left & right              right    left
+                  |                     |        |
+          index   0          ===>       0        1                
+          isBad  false                false    (null)
+    expect = 2 => return left + 1 (return the order not the index of bad version)
+ ********************************************************************    
+ * Summary: return left        
+ */
+ 
+```
diff --git a/binarysearch/_02_FirstBadVersion/Solution.java b/binarysearch/_02_FirstBadVersion/Solution.java
@@ -0,0 +1,47 @@
+/**
+ * Time : O(lgN) ; Space: O(1)
+ * @tag : Binary Search; LintCode Copyright
+ * @by  : Steven Cooks
+ * @date: Aug 23, 2015
+ ***************************************************************************
+ * Description:
+ * 
+ * he code base version is an integer start from 1 to n. One day, someone 
+ * committed a bad version in the code case, so it caused this version and 
+ * the following versions are all failed in the unit tests. Find the first 
+ * bad version. 
+ * 
+ * You can call isBadVersion to help you determine which version is the first 
+ * bad one. The details interface can be found in the code's annotation part.
+ * 
+ ***************************************************************************
+ * {@link http://www.lintcode.com/en/problem/first-bad-version/ }
+ */
+package _02_FirstBadVersion;
+
+public class Solution {
+    
+    public int findFirstBadVersion(int n) {
+        int left = 0;
+        int right = n - 1;
+        while (left <= right) {
+            int mid = left + (right - left) / 2;
+            boolean isBad = isBad(mid);
+            if (!isBad) {
+                left = mid + 1;
+            } else {
+                right = mid - 1;
+            }
+        }
+        // return the order not the index of bad version
+        // if require return -1 for situation no bad version exists
+        // then return (left + 1) > n ? -1 : (left + 1);
+        return left + 1;
+    }
+    
+    // wrap the API call
+    private boolean isBad (int v) {
+        return VersionControl.isBadVersion(v + 1);
+    }
+
+}
diff --git a/binarysearch/_02_FirstBadVersion/SolutionTest.java b/binarysearch/_02_FirstBadVersion/SolutionTest.java
@@ -0,0 +1,91 @@
+package _02_FirstBadVersion;
+
+import static org.junit.Assert.*;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.Timeout;
+
+public class SolutionTest {
+
+    /** Test method for {@link _02_FirstBadVersion.Solution } */
+    Solution solution;
+
+    @Rule
+    public Timeout globalTimeout = new Timeout(200);
+
+    @Before
+    public void setUp() throws Exception {
+        solution = new Solution();
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        solution = null;
+    }
+
+    @Test
+    public void Test1() {
+        int n = 5;
+        boolean[] controls = new boolean[n];
+        int expected = 4;
+        customControls(expected, controls);
+        VersionControl.setControls(controls);
+        int actual = solution.findFirstBadVersion(n);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void Test2() {
+        int n = 31;
+        boolean[] controls = new boolean[n];
+        int expected = 1;
+        customControls(expected, controls);
+        VersionControl.setControls(controls);
+        int actual = solution.findFirstBadVersion(n);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void Test3() {
+        int n = 4;
+        boolean[] controls = new boolean[n];
+        int expected = 4;
+        customControls(expected, controls);
+        VersionControl.setControls(controls);
+        int actual = solution.findFirstBadVersion(n);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void Test4() {
+        int n = 10;
+        boolean[] controls = new boolean[n];
+        int expected = 10;
+        customControls(expected, controls);
+        VersionControl.setControls(controls);
+        int actual = solution.findFirstBadVersion(n);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void Test5() {
+        int n = 10;
+        boolean[] controls = new boolean[n];
+        int expected = 11;
+        customControls(expected, controls);
+        VersionControl.setControls(controls);
+        int actual = solution.findFirstBadVersion(n);
+        assertEquals(11, actual);
+    }
+
+    private void customControls(int expected, boolean[] controls) {
+        for (int i = expected - 1; i < controls.length; i++) {
+            controls[i] = true;
+        }
+    }
+
+
+}
diff --git a/binarysearch/_02_FirstBadVersion/VersionControl.java b/binarysearch/_02_FirstBadVersion/VersionControl.java
@@ -0,0 +1,15 @@
+package _02_FirstBadVersion;
+
+public class VersionControl {
+    
+    private static boolean[] versions;
+
+    public static boolean isBadVersion(int v) {
+        return v > 0 && v < versions.length + 1 && versions[v - 1];
+    }
+    
+    public static void setControls(boolean[] controls) {
+        versions = controls;
+    }
+
+}
