Added solution for binary search in rotated arr and string with spared text

YogenRaii · YogenRaii · commit f8a4f7914afe · 2019-06-21T18:18:35.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SearchRotatedArr.java b/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SearchRotatedArr.java
@@ -0,0 +1,55 @@
+package com.eprogrammerz.examples.algorithm.crackingCoding;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Given a sorted array of n integers that has been rotated an unknown number of times,
+ * write code to find an element in the array. You may assume that the array was originally sorted in increasing order.
+ *
+ * EXAMPLE
+ * lnput:findSin{lS, 16, 19, 20, 25, 1, 3, 4, 5, 7, 10, 14} Output: 8 (the index of 5 in the array)
+ */
+public class SearchRotatedArr {
+    public int search(int[] arr, int target) {
+        int start = 0;
+        int end = arr.length - 1;
+
+        while (start <= end) {
+            int midIdx = start + (end - start) / 2;
+            int mid = arr[midIdx];
+
+            if (mid == target) {
+                return midIdx;
+            }
+
+            if (arr[end] >= arr[start]) { // increasing sequence
+                if (mid < target) {
+                    start = midIdx + 1;
+                } else {
+                    end = midIdx - 1;
+                }
+            } else {  // non-increasing sequence
+                if (arr[start] > mid && target >= arr[start]) {
+                    end = midIdx - 1;
+                } else {
+                    start = midIdx + 1;
+                }
+            }
+        }
+        return -1;
+    }
+
+    @Test
+    public void testSearchRotatedArr() {
+        int[] arr = new int[]{15, 16, 19, 20, 25, 1, 3, 4, 5, 7, 10, 14};
+        assertEquals(8, search(arr, 5));
+        assertEquals(2, search(arr, 19));
+        assertEquals(0, search(arr, 15));
+        assertEquals(1, search(arr, 16));
+        assertEquals(11, search(arr, 14));
+        assertEquals(4, search(arr, 25));
+        assertEquals(-1, search(arr, 21));
+    }
+}
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SparseSearch.java b/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SparseSearch.java
@@ -0,0 +1,67 @@
+package com.eprogrammerz.examples.algorithm.crackingCoding;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+
+/**
+ * Given a sorted array of strings that is interspersed with empty strings, write a method to find the location of a given string.
+ * For example: {"at", "", "", "", "ball", "", "", "car", "", "", "dad", "", ""}
+ * For target: "ball"
+ * Output: 4
+ */
+public class SparseSearch {
+    public int sparseSearch(String[] arr, String target) {
+        int start = 0;
+        int end = arr.length - 1;
+
+        while (start <= end) {
+            int midIdx = start + (end - start) / 2;
+            String mid = arr[midIdx];
+
+            if (mid.isEmpty()) {
+                // traverse both back and front and determine start or end
+                int left = midIdx - 1;
+                int right = midIdx + 1;
+                while (true) {
+                    if (left < start && right > end) return -1;
+
+                    if (right <= end && !arr[right].isEmpty()) {
+                        midIdx = right;
+                        break;
+                    }
+
+                    if (left >= start && !arr[left].isEmpty()) {
+                        midIdx = left;
+                        break;
+                    }
+
+                    left--;
+                    right++;
+                }
+            }
+            mid = arr[midIdx];
+
+            if (mid.equals(target)) return midIdx;
+
+            if (mid.compareTo(target) > 0) {
+                end = midIdx - 1;
+            } else {
+                start = midIdx + 1;
+            }
+
+        }
+        return -1;
+    }
+
+    @Test
+    public void testSparseSearch() {
+        String[] arr = new String[]{"at", "", "", "", "ball", "", "", "car", "", "", "dad", "", ""};
+        assertEquals(0, sparseSearch(arr, "at"));
+        assertEquals(4, sparseSearch(arr, "ball"));
+        assertEquals(7, sparseSearch(arr, "car"));
+        assertEquals(10, sparseSearch(arr, "dad"));
+        assertEquals(-1, sparseSearch(arr, "yogen"));
+    }
+}
